Which metal/plastic nest box to convert to rear roll out?

Any one using Khul nesting boxes with the roll out bottoms?

I am shopping for a metal/plastic nest box that will eventually go in a permanent winter house for about 20 hens. Most of the hens will be large breeds. Will the standard Khul nest be too small? I want to convert whatever I get to rear roll out. Can front roll out also be converted to rear or big bird nest be converted to roll out?

Are there other companies besides Khul that make metal and plastic nests?