So the two aren't specific to each other by any means. I'd say first you need to model and UV the pieces but first you need to decide the basic dimensions of each tile-able element you want to use and how you want to use them. Here are some very helpful thoughts about how a modular pieces could be constructed Fallout 4…
I added a question mark to your thread title. That way people don't think you're offering one, but looking for one. Something to think about for your next thread. Also I moved this to the Allegorithmic forum, where you're more likely to get informed eyeballs.