I've been allowing my rabbits more grazing/play time slowly over the past couple of years. I have no place nor design for colony raising rabbits, but I used to think they were generally safer and healthier away from the ground where parasites, dangerous plants, and predators live. After watching rabbits binky around happily in the yard, nibble on all different green bits, and still live to face each bright new day I am much less protective of them outside. Although I have a large fenced in area, I still confine them to a smaller exercise pen or dog crate so they don't get into too much trouble and I supervise them.
With this change in philosophy, I've been looking into building my own rabbit tractors, which are similar to the pens that folks that raise poultry use. I didn't want to use wood this time around as my raised garden beds are not holding up like I had hoped (built with treated wood). Fortunately, I found a DIY guide for PVC rabbit tractors that looks perfect. Here is the link if it is helpful for anyone else like it is for me:
Building a PVC Pipe Rabbit Tractor