You should take out the grids and connectors and try putting them together so you can see how they work when you attach them from the side or top. The difference is the overlap of the connectors. Since you want to lift the grid frame off the coroplast, you need to make sure that the coroplast tray won't rest on the grids or you won't be able to lift it out. Are you really sure you want to go to the trouble of lifting out the tray? Depending upon what you put in it for bedding, it might be heavy and awkward to lift out. Keep in mind that the tray should be at least minimum standards for the number of guinea pigs you have. If you use regular bedding, you can line the cage with newspapers or paper yard waste bags that you cut open to lay flat. When it's time to clean the cage, put a hefty bag in there and roll the bedding into it. That's what I do when I don't use fleece. I have a double decker cage and the bottom of the top level is 28" off the ground. The top of the grids are 42" off the ground. I have no problems cleaning it without removing the base. There are a lot of good photos of different types of cages in the photo section. If you make a lid, you should overlap some grids on the three sides so it doesn't fall into the cage. Your other option is to add I-beams for the lid to rest on. I attachthe lids to the cage with zip ties when I've built cages with covers.