Do you mean wood shelving or plastic shelving? It can be difficult to find good shelving. Ranchouse cages on ebay make a variety of sizes of pine shelf. I've had some of theirs. They come ready with fitments and are plain pine and can be painted. I do find them a bit heavy though and they can unbalance a cage a bit, depending on how big the shelf is and where it is.
Savic make a plastic corner rat shelf.
The best shelf I've had was from Amazon in Germany - but I don't think they ship to the Uk any more for that shelf.
Is it for the Alaska?
Plasti-kote - you want the water based enamel paint, which you brush on with a small paint brush. It goes quite a long way so one pot would easily do two coats on a shelf or maybe a bit more than that.
https://www.amazon.co.uk/s/ref=nb_sb...ti+kote+enamel