Meshing a cage is an option but as Cypher says, it can be very tricky and it needs to be safe so no sharp edges a hamster can get caught on. From what I've heard you can cut your fingers to ribbons cutting the mesh and turning the sharp edges over. Some people say meshing should be done on the inside, or the hamster can get through the bars and get trapped under the mesh. If the mesh is on the outside you would need a lot of cable ties to make sure the mesh is well and truly pressed onto the bars and no areas a hamster could get trapped under.
The other option is diy cages, but to be honest they can often work out as expensive especially when you need to buy plexiglass.
I also forgot to mention bin cages
If you don't mind the idea of meshing, then a bin cage would be easier than meshing a cage. This is a good sized bin for A robo - about the biggest one I know and it's supposed to be good quality plastic for cutting (some bins crack or split when cut). There are lots of tutorials on youtube for making bin cages.
Really Useful 145 Litre Clear Stacking Storage Box with Locking Lids