Dividing a Detolf would make each half even smaller than an 80 x 50 cage,so it really isn't worth it if you want to divide cages that way.It would take up more space and offer far less room than stacked wire cages as well,so keep that in mind anyways.
Making lids for cages is a very easy thing to do
You do need to be careful with cats but I'm sure there would be a way to secure lids with velcro instead of not using anything,or some other method.All it takes is wood,mesh,a stapler,and a way to screw the wood pieces together.