I'm doing something like what you're asking about, only different. I'm starting to breed four different breeds of bantams, each breeder pen will have a roo and four hens. So today I built the first breeder pen for the BB Reds which looks very similar to this:
When I build the next pen for the Crele bantams the left side of the first pen will be the right side of the second. Then I'll add a third and a forth. The cool thing about this setup is that I built this first pen in a day with all brand new high quality materials for about $75 total. I think the addition of the second pen will cost about $40 dollars total and I should be able to build it in less than a day since, as I said before, the two pen will share one side.
I did make some design changes and will have pics posted in a new thread tomorrow. All I have left to do is put my wire on the doors.