That sounds good. Agree with Cypher that the 145l rub bin is a great bin for a bin cage - a good size for a robo - they can be very active. The Samla bin might be fine too. They can climb bars at night when you can't see! Our robo used to climb them if something scared him as well. If they climb to the roof it's a long drop if they land on something hard.
Making a full level is not that easy in my opinion! So a bin cage sounds better.
This is the rub bin. It's not as cheap as the Samla bin but reports say the plastic is much easier to cut and doesn't crack like some bin cages when cutting - it is also stackable with a good lid.
https://www.wickes.co.uk/Really-Usef...-145L/p/143494
Floorspacewise it's much better than the Samla - nearer 80 x 50 internally and less sloping.