Steadfast, and Headstrong
I do believe he's trying to -make- one, not -join- one.
I suggest contacting some of your Xbox live friends and see if they'd be interested. That's usually one way to start out, then try and see getting a few people interested while online.
Ask them if they're in a clan or interested in joining a clan, then say that you're recruiting for whatever your clan's name is, and go from there.
As for a clan base, I find that taking credit form already-created maps isn't that good, so creating your own from scratch is highly a must. Just think of something you want in the 'base', start creating it, and add to it from there.
--I always start with the meeting chamber, like a stage at a concert, or something. If you see something you don't like, change it and experiment with other items you can use.
You would also use already created maps like Sword Base and Boardwalk and just add to them to make it unique for your clan.
[Edited on 05.16.2012 7:22 PM PDT]