You can just use a big mound of torn up strips of plain white toilet paper for nesting - put a heap in the cage - they like to pouch and take it to their house to build the nest with.
We have a robo as well and I know finding the right cage is difficult. I went for a tank style but am wishing I had a cage now as I can't get on with top only access (especially as our robo is very nervy and not tame).
I wouldn't go for 1cm bar spacing with a Robo. You could use something likethe Barney (if it's not too big for you) but I think it would need a full levelor a lot of extra shelves as it's quite tall (that has 7mm bar spacing).
My choice for a Robo would be:
Smallest size:
Duna Multy - perspex tank - bar spacing on top is 7mm ish and fine. Personally I think it doesn't offer a lot of scope for enrichment and something a bit bigger would be better, but some may depend on the personality of the robo. They are very active generally.
https://www.portonaquapet.co.uk/shop...a-Multy-M36261
Maxi Duna multy - the bigger version - I think this is better and you can fill it up with toys, tunnels and have a digging end. But it's quite expensive. Postage is on top on this site so makes it a similar price to Amazon price (Amazon sell it too).
https://www.portonaquapet.co.uk/shop...a-Multy-M58956
Kerry Terrarium from Zooplus. I got this for our Robo - it is marginally bigger than the standard duna multy (first cage linked) and taller so you can put deeper bedding in. This was my compromise cage space-wise as already have a 100cm cage for our Syrian. It's ok but I'd prefer a cage with a door at the front for easier access and taming.
The grid doors on top of the duna tanks are probably better.
Hamster Cages: great selection at zooplus: Small Pet Terrarium Kerry
If you prefer a cage to tank style I think this one is just right (I've used it before for a Syrian) and am thinking of moving our Robo to it. But it is also expensive.
It's the same cage as the Hamster Heaven - identical dimensions - but only has 7mm bar spacing so suitable for mice and smaller hamsters. The metal grid shelf needs to come out - not suitable for hamsters' feet. I used a flat roofed house instead of a shelf in it. It has the low height of the Hamster heaven too and a good sized base for substrate, plus a big front opening door. It is expensive, but cheaper than the maxi duna multy and a good size - not too big, not too small.
https://www.amazon.co.uk/Savic-Micke...ic+mickey+2+xl
Depending on your budget, and how much space you can make for a cage, a Detolf is also an option
Ikea glass cabinet tipped on it's side with the door left off- a bit of diy involved in making a lid out of wood and mesh but there are plenty of tutorials for that. It costs £50. Some people stand them on top of Kallax units for storage underneath or a couple of £5 Lack tables.
DETOLF Glass-door cabinet Black-brown 43x163 cm - IKEA
https://www.google.co.uk/search?q=ha...w=1252&bih=553