You can find the measurements needed
http://www.guineapigcages.com/howto.htm. As far as making a new post, get out of this thread and go to the sub-forum you want (i.e. "About Cages" sub-forum). There will be a list of different threads and at the top of them on the left there will be a button that says "New Thread." Click that, make a subject line, then type to your lil hearts content.
Johnny