There is website that SCARM supporters created with some O gauge buildings and I have collected some other building files that some forum members have created. I can't find the bookmark or remember the site - I'll post it when I find it. Forum member Chiloquin Russ created some excellent structures also.
Heres a couple building files attached. Open them in a separate instance of SCARM, selected and copy and paste onto the layout that you are working . You can set the elevation is the properties of the building and right-clicking and rotating will position it.
here's the last file with the Lionel Rico station, a Korber 304 Diesel shed, the Atlas 6907 Lumber Yard Long shed and Sales Office and a Lionel Quonset Hut.
A second shot with an SD38-2 and train from the SCARM simulator
Some of these cats are good with 3D tools. Forum member ACE made some cool structures, engines and cars.