Well...I was mostly talking about expanding the roof line if you were planning to leave it mostly wire. If you're going to box most of it in, then keeping the rain and snow off won't be an issue, so I'd leave the roof as is.
Can you get some better pictures of the structure? When I click on...
So 12 birds total? You didn't mention the dimensions. With 12 chickens, you'd want about 10 linear feet of roost space (normally you want about 12" per bird, but some of yours are bantams. Remember...it's not about just roosting - they should have room to flap up/down/turn around, etc. while...