While hay is the most important ingredient in a guinea pig's diet, it is also the messiest. It can present challenges for cleanup, especially if you use fleece for bedding. With fleece bedding, the less hay you have strewn around the cage the easier it is to cleanup.
I made this hay rack/box from leftover coroplast. It is 30 inches wide, 9 inches deep at the top, 2 inches deep at the bottom, and 11 inches tall.
The litter boxes are veggie baskets and tubs. This has worked out very well for us and our guinea pigs. I put wood pellets on the bottom tub, put the basket in place and add hay. You could use carefresh or other bedding. It keeps hay and poop separated from the litter. It's so easy to clean. I just take each basket out, dump it and wipe then add some hay. The basket/tub is 10 x 13 inches each -- a perfect size for each pig. You'll need to improvise on finding some bins that work for you. I found mine at a chinese grocery. You could try a dollar store or kitchen supply store. You could also use cardboard boxes and just toss them when soiled.
This is my 2nd one for this design. I made the first one with the big holes on the bottom, but they managed to get inside and pee all over. I had to throw that one away. So, this is the new, improved model and cavy-cleanup tested. The hay bin sits on top of their individual tubs, so the tubs do not tip.
Notice that the 3-cavy version is wider than 2 grids! So, if you have a 2x4 GRID-sized cage, for example, you would need to mount this hay rack on the long side. Just shorten the template as needed for a 2-cavy or 1-cavy sized hay rack.
This style of hay bin has the advantage of safety over grid hay racks, especially when you have small guinea pigs. Also, it's a bit easier for the guinea pigs to get to the hay, which is important, while still keeping the cage fairly neat.
This is the tricky part ... just dealing with the template and the measurements. Remember, measure twice so you only have to cut once.
Score the lines on one side. Carefully cut the window holes out using an exacto knife or sharp blade.Here is a link to a PDF version of this image so that you can print out the template for better review.
Fold the back up with scored side on the outside.
You will need to cut the 2 inches on either side of the long end piece on the bottom to allow the tabs to be folded up and the front back to be folded up as well.
Fold in the back flaps.
Fold up the bottom tab. You can secure the coroplast with some clear packing tape.
Fold the front ends back over the back side and secure with packing tape.
Secure the completed hay bin with binder clips to the cage grid wall and insert hay!