Griffith Observatory (Western Themed)

So here is what I have so far with my Western Themed Griffith Observatory. It's pretty basic and not a lot of detail right now, but I am still working on it and trying to add things to it to make more life-like. My goal is to add things like a door and windows and maybe some kind of door or entry on the two smaller towers on the left and right. I'm having some trouble with Photoshop and getting rid of the seam that is on the back parts of the towers. I'm not sure how do to layers and get the image to look how I want it to. This is still a work in progress and I hope to get as much done as I possibly can.

Textures I'm working with:

References:

http://martinconceptart.blogspot.com/2011/04/blog-post.html