If you want to show the actual external walls only then it is just a matter of layer control.
Make sure the wall are in a layer that can be turned on for your site plan and turn off all other wall layers.
If you just want a single line for your building perimeter then I would magic wand or draw an empty fill around the external of the building and then make sure that is in a layer that you can see on the site plan.
The advantage of a fill is you also can then determine the area of you building/s and can even schedule them.
I use fills with different IDs for all the different building areas (main building, garage, workshop, courtyard, etc.) that I can then list in a schedule for the areas.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11