So I just started using Sketch up recently and was surprised how easy it is to use. These are the first items I've ever made in it... but still I think they are fun for just messing around. Everything snaps in grid mode. The are lots of 100x100 blocks of different heights so as to make paving at different heights easy, as well as 6 sloped blocks, 3 which are for sides and 3 for corners. The are also 6 sloped blocks with windows for the sides and corners. There are two sets of stairs and a little concrete barrier thing. The zip file is attached to this post.
The textures I got from CG textures. I would love to give you permission to use them commercially, but due to the fact I'm using the free version of sketch up I can't really do that until I buy sketchup 2015 (hopefully in a month or two or something, then I can give you permission to use them commercially) But still, have fun!
Edit: I will be working on this pack in due course and adding more detail to the models, if anyone has any request for segments let me know and I'll try to make them.