In assembling most the buildings for my layout, one of the things I do is get rid of the base. Most bases aren't just foundation pieces, they've got extra details moulded in them.
This policy, however, has caused some problems. The bases are a key structural element that keeps the building from warping as badly. So if you avoid the bases like I do, consider building an internal base using styrene pieces. Not only will your buildings not warp, but you'll have something on which to add a floor or other interior details.
Puckdropper