Okay, here goes! Stack one Bin on top of the other. Make sure the `lip` of the upper bin sits in is secure and solid and doesn`t wobble around or show any gaps. Give it a jiggle about just to be sure.
Looking at both stacked, decide what you want to do. Mesh the front of both bins for good ventilation and visuals of your hamster and ease for hanging a water bottle in both upper and lower floors? If you done that, you may not need to mesh the lid itself and just clip that on. Or mesh the lid as well but it shouldn`t be necessary if you measure two oblong squares at the front, making sure you leave the lower bits deep enough for your substrate not to spill out!
That should be it really. I would use small bolts, nuts and washers though on the grills to make them very secure and have the flat screw on the inside and the poking out bit on the outside unless the screws are very neat and short. Also have the mesh fitted to the outside of the Bins as any sharp edges won`t be near the hamster. I`ve seen some people use duct take around the edges but if the mesh is on the outside (cut it bigger than the hole it`s going over) it will be safer.
You will also need to measure and cut a square in the upper floor for a ramp to go up to. Just measure a square, mark each corner with a pen and melt holes using a metal knitting needle heated on a gas ring. Then use a hand held blade or craft knife to remove the middle section. Go slow with this though and take your time.
Make a long plywood ramp and secure two hooks in the top of the wood. Melt two holes at the top for the hooks to fit into and you have nice wide wooden ramp.
Think it through before you do anything. Take your time and just do a but at a time, probably starting with meshing the front panels. x