How to generate a surface for Building Area calculation

Hello All,
I am trying to calculate Building Coverage Ration = Building Area / Site Area
But I have difficulty getting Building Area as single surface.
The Building Area we want is like 12 pm sun cast a shadow on the floor. So the Building area includes roof, balcony, and extruded surfaces.

Trying to get Building Area B as image shown below.

You could use Drape from the Sandbox tools.

I added guidelines just to show that a balcony would be included in the draping process.

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Here’s a moving version of what Dave suggests showing that it can be multiple buildings and you can use the left over area to work out your coverage.

Hello Box,
Nice method,
What I got has more complex building which does not properly drape as I hope.
Is there way to get a clean surface like the blue line without all the inner lines

Yes, as it is something simple in my opinion it is easier to do it manually:

  1. draw a rectangular plane at the bottom of the building;
  2. select the line tool, pick up points on the corner of the building and extend the lines until they reach the rectangular plane
  3. do this until you have all 10 or 20 surface corners that you want to draw
  4. close the surface

It is even easier than that.

  1. Draw a large rectangular plane some way under the building.
  2. Select the Line tool.
  3. Hover on the large plane until the “On Face” tooltip appears. Then push and hold down Shift.
  4. Now start clicking on corner points on your building while still holding down Shift.
  5. Finally close the resulting shape
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If you choose to use Drape, make sure the perimeter of the building outline divides the large rectangle into inner and outer regions.

Delete the outer region, use ThomThom’s CleanUp3 to delete coplanar edges and you should be left with the area you are interested in.

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