Cage door and other questions

My husband and I are trying to buy the materials needed to make our own C&C cage. We have ordered the grids and connectors and will be contacting a sign shop for the coroplast. We are planning to build a 2x3 grid with 2 stories. We must have a top on our cage and also doors seeing that we are trying to keep two poodles and a toddler out of the cage. Can anyone here advise us on how to make the doors? I had seen cages on ebay that had spring doors but we aren't sure how to make these and what materials would be needed. Also, we need advice on making a top to the cage. We have had our new guinea pig, Dippy, for a week and he is in a pet store cage which is way too small. We are new to owning guinea pigs seeing that he is our first and had no idea how much room they needed until I stumbled upon your site. Any advice and ideas on making the cage will be greatly appreciated.