Issue:
Revit is an efficient authoring tool for the AEC industry; however, users face difficult challenges when there is a demand for major changes on short notice. Although Revit is efficient, depending on the modeling approach, changes can be very limited and may require a significant amount of time to revise the model.
Causes:
Unfortunately, there is no single root cause for this issue. It primarily depends on the user’s experience with Revit and the AEC field. The more experienced a user is, the more the modeling technique can improve the efficiency of model revision per changes.
Solution:
I will present some basic concepts on how to control the model so that users can effectively adapt to any changes in the model.
Case #1:
Wall thickness needs to be revised due to design changes or code requirements. The user updates the walls, but the required corridor width for public ways no longer meets the requirement due to this update.
If the user understands how walls behave concerning their location lines, this change would have minimal impact. See below. 
The wall family has a unique parameter that determines wall behavior when thickness is changed. The following example demonstrates different wall behavior depending on the location line setting.
It is also very important to know where the exterior and interior sides of the wall are.
By changing the location line of the wall to "Finish Face: Exterior" and having the exterior side of the wall face the critical width, the user can maintain the critical corridor width even after the wall thickness changes.
Case #2:
Revit is all about initial settings before modeling begins. You can utilize groups to control repetitive elements in the project model. A good example would be unit modules for an apartment or hotel complex. If you have multiple different unit variations for an apartment project, it would be efficient to put each unit into a group.
Start by setting the group control view off to the project site.
Then create a group control view that will be used for controlling all model groups in the project. Once all groups are placed in the proper phase, set all groups to be demolished before existing. This will prevent any elements in the group template from being added to the schedule.
Case #3:
The Design Option is used to present alternative designs. Many Revit users appreciate this tool; however, having too many design options comes with a high risk of encountering a rigid model, leading to various challenges such as graphic display issues and difficulties in modifying the design in case of major changes. The best way to avoid these issues is to simplify the Design Option.
Instead of blocking small sections of the model in the design option, consider dividing the design option per floor, especially for interior walls, furniture, and casework. This approach helps maintain the simplicity and flexibility of the model.
Case #4:
Roof construction can be a stressful task in Revit when there are major changes in the building footprint. Here are a few tips to minimize the impact when changes are needed.
The best way to make a roof flexible is to build it in multiple segments rather than constructing the whole roof in one sketch. The following is an example of a complex roof.
Building the above roof in a single sketch would be difficult and may not even be possible. Also, it gets more complex if the roof slope needs to be varied. However, by dividing the roof into each slope segment, constructing a complex roof becomes much easier, and the user gains more control over the roof.
Segmented roofs can also show that the roof slope may not work with the original design, and the designer needs to update the roof configuration accordingly.
Case #5
Often exterior wall finish transitions forces model author to slice the walls. However, slicing the wall come with corner join challenges if adjacent joining wall heights are different.
The best way to manipulate join condition for such conditions is to using disallowing join option and manually joining the walls.
Join Geometry 
Wall join is cleaned up using above method.
Case #6
Families are critical components for Revit modeling. Many users prefer multi-configuration families over single-configuration families due to their convenience. However, multi-configuration families can be a double-edged sword, potentially having a significant impact on your project model.
The image above shows the file size differences. Table 1 and Table 2 family files are approximately 450 KB each. The table.rfa family is a multi-configuration family that combines the Table 1 and Table 2 families. It is about 200 KB larger. While this isn't a significantly large family, these families contain only geometry without any parameters.
A simple way to approximate the impact of a family in the project is by looking at the family size. Let’s assume that the table families are used 3,000 times each in the project. If the family was a multi-configuration family, each family would be 650 KB. With a total of 6,000 families used, that would be 6,000 * 650 KB, summing up to approximately 3,900 MB.
If a single-configuration family is used, it would be 6,000 * 450 KB, summing up to approximately 2,700 MB. This is almost 1,200 MB smaller than when using a multi-configuration family. If the project is small enough, this might not have any impact. However, if you are working on a large, complex project, this can significantly affect the project's performance, even if the model is built perfectly without any warnings.
Case #7
Workset is one of the key Revit features that allow multiple users to work on the same project file. Creating organized worksets can help save many production hours and increase productivity.
There are several benefits to utilizing worksets, but one benefit that is most notable besides worksharing is visibility control. Using a filter to target larger groups of elements can be a daunting task. However, if a workset is used for larger group visibility control, this can be easily done.
Example:
If a model author wants to hide highlighted elements on all floor plans, it would take many hours to go through all plan views to hide them manually. If a user wants to use a filter, it would require complex filter settings to apply to all floor views. The easiest way to control this would be by using a workset and turning the workset off on the needed floor plan views.
Case #8
View templates are a critical tool for flexible modeling. Too many model authors are wasting their valuable production time adjusting the visibility in the views manually. Manually hiding elements in the view should only be allowed in your working view or for a handful of items within the entire project duration for special conditions.
Revit prioritizes manual overrides. If any element is hidden manually, the only way to bring it back would be through a manual override. If a view template is used for the view containing manually hidden elements, they will stay hidden whether there is a view template or not. This makes it extremely difficult to control the visibility when large changes need to be made within a short time and leads to documentation errors.
Organize the project view templates and make sure to use filters and worksets to control the small sets of elements that may need to be turned off for specific views.
Case #9
Controlling a model with schedules has huge benefits and serves as the baseline for flexible modeling. To manipulate the model using schedules requires a clean and organized modeling system. All the topics discussed above are part of this system. Below is an example of an organized modeling system.
Conditions:
- The model author needs to differentiate exterior doors from interior doors with different colored lines.
- The project is a large campus project with multiple doors.
- The project is still early in the stage, and only a couple of multi-typed families are used to represent the doors in the facilities.
- There are about 390 doors that the model author needs to reorganize and color.
- All exterior doors have widths of 36” and 72” and are already properly placed in the model.
The above conditions are a great example of utilizing schedules to manipulate the plans. Using the description parameter, the model author can differentiate between exterior and interior doors.
Updating the parameters for 390 doors can be time-consuming. The easiest way to update this schedule is by organizing the schedule in bulk by turning off the "Itemize every instance" option in the schedule.
Disabling this option will condense the schedule and sort it by Family and Type, as shown below.
Per the above condition, all exterior doors are 3’ and 6’ wide. Update the value of the Description parameter, and this will update all doors of the same type at once.
Once you have updated all values, you can apply a filter using the same Description parameter to color all exterior doors "Red."
The baseline is that the model needs to be built with consistent quality. This is key to successful flexible modeling, which will save many production hours if done correctly.
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