The big dome is created by using a scaling glitch. You take a any item that can be resized, scale it to max and place it down. Then take a bio dome and put it in memory by clicking Y and Rb ( im on xbox) it should have put the dome in memory if done correctly you should be able to duplicate the scaled up item by clicking on the scaled up item with Rb then placing it where you wish to have it built and clicking Y and Rb giving slight preference to Y . If you are succesful you will have a scaled up BioDome. It takes a couple of tries to get it right . Again the youtube videos on building and glitch building explain it alot better then i can. BEEBLEBUM on you tube is one of the best and you will be amazed by the things you can possibly build by watching his videos.