Available as kits from https://candcguineapigcages.co.uk/
or you can also find supplies & build your own via Amazon or Ebay & correx sheets are available via Ebay or any sign makers. You'll most likely want to also cable tie each grid to secure them as the connectors can be a little unsecure sometimes.
IMPORTANT: grids should have 9 squares horizontal & vertically. If the grids have less thatn 9 squares then the squares will be big enough or smaller guinea pigs to escape or potentailly get stuck & hurt themselves.
Our favourite place to get online delivery of Hay! And what's even better is, if you mention Worcestershire rabbit rescue and friends in the 'where did you hear about us' box, healthy herby will donate hay to our rescues ?