Expanding cages is always awesome! When I adopted Bridget and she had babies, I went from a flat 2x4 to a 2x6 with 2x2 loft and my piggies like it and I love the hay loft. If you have two boys, I'd definitely go with the 2x5, just because that's the preferred size for two boys, but if you have two girls or a mixed pair then you could consider the loft. If you do go with the loft, I'd recommend a 2x2 loft just because it has space for the piggies to move around without causing fights, but also realize there is a possibility they won't use it no matter what the size.
If you want to expand the base level, you have several options for the coro, and then you'd just need the extra grids if you don't already have extras.
1. If you made your own 2x4 and still have leftover coro, you could use packing tape to make it longer for a 2x5.
2. You could also just get a new sheet of coro, which could be as cheap as like $15 if your local Home Depot/Lowe's carries it (this is probably the cheapest option!), but they'd only have white and maybe translucent, so if you want colors it would be likely closer to $35 at a sign shop.
3. If you don't want to DIY you can get the pre-scored coro from the Cages Store without buying more grids, just look under "Coroplast" and you can buy any size base.
If you want to do a loft:
1. Order a loft kit from the cages store (I did and it's awesome!)
2. DIY and get coro and grids and determine how big of a loft and then you'd cut the coro and build it on top of the cage, and once you get to where you know what you want to do we can help more. You'd also need to figure out a ramp. I think there are tons of pictures on here so you could try and DIY it, although I'd definitely consider getting at least the ramp from the cages store unless you're a serious DIY-er just because that's the most finicky part.
I'll definitely look into this more!
