Take a look at the level design tutorials from epic games: ?v=I8WBF4AyAX4&list=PLZlv_N0_O1gaCL2XjKluO7N2Pmmw9pvhE
Normally you dont have to convert a bps to a mesh, but when you do it, you just have to make sure that the lightmap resolution from the mesh isn’t 0 and when there are still some errors, you will have to create/generate a 2nd uv channel (?v=z5yc-bKbHyc). Also make sure that you add a skylight into your level so that the shadows aren’t so dark anymore
And of course when you have some special problems you can just ask your question in the forum 