Looking good. Firstly, I want to comment on john.d.h's orc. I think that orcs were grey, in Lord of the Rings, but they were supposed to be swarthy, which means they are very dark. Brown probably isn't the best. The Uruk-Hai were a superior, taller, and smarter race in LOTR.
Secondly, I don't think orcs have anything to do with trees. They lived in caves and plain-dwellings in the rocky crags of Middle-earth. They were banished there for prior involvement in conflicts. The buildings probably should be either tents, simple bone structures (not much wood on a harsh mountain, to be truthful), and caves. They are hunter creatures, and so would probably use any and all parts of their prey to better themselves.