You can downlead a free 30 day trial copy of Filter Forge, which is compatible with photoshop and has a library of over a 1000+ texture presets you can download and mess with. It creates seamless tiling textures at the click of a mouse too, and very nice ones.
I can probably help you with the building/texturing if you like. I mainly build prefabs so I'm used to working with megaprims and getting the maths right to make things fit. I'm no mean texturiser too
