I know that on the mid level, you can only build to the blue line of stone. I don't think that you can go higher than the game will let you. Most shops can have a second story. Give it a try.

zeldamerchant

 

Yes, all shops have building limitations. It varies on the shop, so there is no concrete answer, but basically every shop is built to their max size. Also, you can't have working redstone, flowing water, or naturally grown trees.

 

if you do /rg i station1, it will show you the dimensions of that station. just change the number to see the coords of the station that you're interested in. All of them are boxes with a limit on the height. there are many different sizes though. Some are only 5 high, but I think some are 8 or more high.