Compiling with -final might remove the black: http://imgur.com/oL7paSz
Are the bricks made of dirt or is the dirt made of bricks? http://imgur.com/pUNOpv9
You could place a decal below the tree: http://imgur.com/6SN8PEX
Stairs could use some playerclip: http://imgur.com/5ppQm1l
Examples of things you should func_detail: http://imgur.com/Cl0CxW2 http://imgur.com/WB87ZRI http://imgur.com/zdaAfno http://imgur.com/JxyB5Aq
Floater: http://imgur.com/Y5HAiCo