How to deal with the collision of a complete huge building

As a newbie,I wanna know you guys about how to deal with the collision of a complete huge building such as a skyscraper with inside walls.If I import it,the collision would be messed up even I dragged the [accuracy] in [convex composition] to its maximum.I wanna know that:

1.Is UCX_ the only way to deal with this kind of condition?But this building only includes walls and stairs and it doesn’t have very complex shapes.(In fact I make it from a CAD blueprint)

2.UE4 official tutorial says that:“Blocking Volumes can be used in the place of collision surfaces on Static Meshes, particularly in the case of walls in structures. When used in this way, they generally have a few advantages over mesh collision surfaces. The first is that they are easier to calculate than more complex collision models.”(in the chapter Volumes User Guide).But I didn’t find a way to automatically match blocking volumes with imported model.

3.Or some way to convert static mesh to BSP