When I 1st bought my C&C cage, I assembled it with the loft as provided. My piggies never used it so I removed the ladder and now use this loft area as storage for their hay and forage.
I then realised that my piggies liked an area above ground so I have put a grid half way up - very similar to the balcony. Mine has a layer of correx on the base. I use one of the pet houses that are readily available commercially and they have a little area at the front which is ideal for putting straw to graze on.
I would advise anyone who is thinking of bespoking their C&C cage to have a good look at the threads on this forum. There are quite a few dating back quite a few years. It's really great to see how imaginative people have been and you will get a lot of good ideas.
Whatever you choose to do , please ensure that it is safe and is easy to clean. I am trying to upload some pictures of mine but am having some difficulty. I am going to post this reply and will try to upload the piccies later.