
The home made ones I have seen have been made of white furniture/contiboard and the front has a lift out part that allows Mum to get out but keeps the pups in, the pig rails have either been a ledge a few inches up the sides or plastic pipe instead.
For my first litter I used a puppy pen from Doghealth, at one end the base of an under bed storage box as the bed with the heat pad at one end of it, when the pups started getting out of the bed to wee etc. I swapped to this tray from B&Q which was for potting plants up on, it had 3 sides and an open front and worked very well.
Now I have one made by Linkabord with base and pigrails, made from recycled plastic, can be colapsed and stored away and the pieces soaked in the bath to get rid of germs or hosed down if needs be, the B&Q tray is still used when pups are a bit bigger.
Alot depends on the breed size and the number of pups there is likely to be.