Ours is a UPVC made by a company called Steelcity, they advertise on ebay, half the price of snowsilk and just as good, depends on how many litters you are plaining, have had one cardboard one it latested 3days, bitch dug her way through bottom. 30" 30" plenty big enough for a cocker,
A hand made MDF, lined with vinly tiles does the job, we used one for 3 litters succesfully, good luck