I have some thoughts on the roof...
First, a "dome" will be very difficult, because from the current top of the outer wall to the very top of the map there is only room for 9 blocks up.
I'm personally not extremely fond of the dome idea, but that is just my personal opinion - obviously doesn't mean we can't do it. I kinda like the natural view above, but that's just me.
I actually don't think we need a "roof" at all to be honest --- once we finish the wall design I think it will be virtually impossible to get over it. I have a design that from the current top of the wall, goes inward a few blocks, and then up several blocks - even if someone could manage to get to the outermost top portion of the wall, there would be no way for them to get up enough blocks to get over the inner small portion of the wall at the top (hope this makes sense).
Rather than just go straight up and stop, I have some ideas for making the top look nice - but haven't tried any yet. Obviously this can all be open for discussion.
Plots are still 12x12 for now, as far as I know, with possible option to 'purchase' additional room from J3sus.
I also propose that all construction in the new area be temporarily halted until we get wall completely up, old wall torn down, and the streets laid / layout organized as mentioned in kperk's previous post.
All just my thoughts