Here are some shots of a single floor, with some posts that will possibly support another floor, or perhaps just a floor tile as a roof.
I think that these pieces will be good enough for the kitbash, but I want to make a ladder that will to with it. Here's a mock-up:
Basically, two long thin logs with some small logs crossing it. It's all tied together using rope. I'll probably try to design it so the openings are wider (for minis) and the rungs might extend out a little more, in case you feel like having the extra detail.
I'm thinking about possible rails - I was imagining I'd need something to hold the tile on, but it seems fine as-is, and fiddly railings fall apart when you try to pull them out of the tile. Still, I might be able to make some low railings out of logs or wood (maybe just using the floor texture) to make the tower a little more "finished" - it'd be more like a fort.
But, in an effort to get things into the hands of the kitbash judges sooner, I'll wrap these up and do the railings (and maybe a small roof) for another kitbash.