Building lights is devastating my map

Hi all,
I am importing some asset into unreal 4. This is some house, it looks like this:

I know some materials need correction (they are white). Problem is after light build scene looks like this:

Anybody can help me?

P.S. By the way entire model is a single mesh.

Ok, I am back and I have bad news - reason is not overlapping uvs. I’ve used unwrapping software - no more overlapping uvs, but result is still terrible. Look at posted image please. You see rather simple room mesh - only walls and two windows. UVs do not overlap. Whole mesh uses one big texture (4096x4096). I’ve used option allowing unreal to generate lightmap uvs. And still after building lights the result is sh**! Is it possible to import and properly use architecture objects in Unreal? **** if it requires me to import single walls and split meshes to thousand parts I better use some other engine.