This is a bug, and not a feature. In regards to your suggested build UI, I prefer the click-and-drag method because it lets you get super precise and detailed with your builds.
There are templates that you can use to make the perfect canvas image for some of the canvas items (note that the thread is a bit old, so some of the newer canvas items probably don’t have a template). Just use an image editing software to get the canvas image exactly as you want and host it on a site like Dropbox or Imgur.
Your condo is also your server. You make the rules; just be sure to be careful about what you say in chat, as that may be connected to a lobby server which does have the right to punish you for breaking their rules. Remember, you can hit TAB while chatting to switch between global (communicates between all connected servers) and local (communicates only to those in your immediate server, in this case just people in your condo) chat.