I have 4 x medium and 4 x small mice / small animal boxes which I can sell because these are the ones I started with and I've changed to different types. Both types stack on top of each other they're the same as the ones here
http://www.plasticboxshop.co.uk/pack-of-4-50lt-smart-storemaster-box-with-clip-lid-397-p.asp
So they have clip on lids which open both ends. The "medium" boxes are 35litre and the "small" ones are 12litre they all have meshed lids, a side "window" and an end "window" £8 each for the medium ones and £4 each for the smaller ones I'm in Kent
Will take pictures in a minute 
http://www.plasticboxshop.co.uk/pack-of-4-50lt-smart-storemaster-box-with-clip-lid-397-p.asp
So they have clip on lids which open both ends. The "medium" boxes are 35litre and the "small" ones are 12litre they all have meshed lids, a side "window" and an end "window" £8 each for the medium ones and £4 each for the smaller ones I'm in Kent