It looks like a solid build, very haphazard and orky. The color is a little too uniform, for an ork tower I'd expect discoloration, stains, moss, blood and worse. A few skull caps or scalps hanging off the structure would also fit right in. The only thing I don't like is the roof, it looks a little too blocky for tile. For watchtowers, I've found leaving them topless (woot!) makes mini placement easier, or you could go with something like animal skins; paper soaked in diluted white glue and stretched over a frame comes out pretty good.
your decoration will Be prettier if there were more color and if your grass were less uniform. you can put some green on Wood so that it appears wormeaten and some craniums for a ork tower will be obligatory