the weird thing on your roof is just your normals - select the face and use the set to face normals tool.

your best bet for UV mapping your house is to use planar mapping - it should be relatively easy. take a look at this tutorial which will show you the basics of UV mapping.

https://www.ramyhanna.com/texturing/p...utorial01.html

as for applying different materials, you can apply specific shaders to certain faces - your best bet tho is probably to just seperate the various pieces - so make your concrete part out of one model, your metal piece from another, and so on, and then just create specific shaders for each. do the tutorial and start experimenting and it will begin to make more sense.