Ranchouse cages on ebay sell shelves in all different sizes.
They do these two shelf packs as well. To be honest I only used one or two of the smaller shelves. The screw on bendy bridge ramp is quite good. For smaller shelves just to cover a gap or something. They do larger ones and you can choose the size/width. They're a bit slippery on top so I roughened mine up or put hemp mat on them. They come with all the fittings but may be cheaper to make one yourself.
https://www.ebay.co.uk/itm/Mixed-8-P...kAAOSwNuVaxzj4
https://www.ebay.co.uk/itm/Mega-Pack...4AAMXQlgtSwVvI
https://www.ebay.co.uk/itm/4-Pack-5-...EAAOSwpXNaxz7p
https://www.ebay.co.uk/itm/25cm-Deep...n_g_kxy4jpELSg
This one you select the size/width
https://www.ebay.co.uk/itm/25cm-Deep...n_g_kxy4jpELSg
This is their page with all the shelves
https://www.ebay.co.uk/sch/m.html?_s...Shelf&_sacat=0