Thanks for all your help and suggestions.
I think i am going to double the weld mesh up with 16g 13mm sq and 14g 25mm sq on the outside. Its going to be expensive to have both but worth it for the buns safety and our peice of mind. This will be to top, sides and bottom of the runs.
Hutches will be 6ft by 2ft by 2ft, constructed of 3" sq fencing posts and 12mm exterior plywood. Felt will go on the roof which i am going to overhang by 6" on all sides of the hutch. I may even mesh over the top of the plywood .Mesh on one of the doors with heavy duty bolt locks and padlocks.
I will add some legs to lift the hutch about 1ft off the ground. The hutches will be put on a pressed concrete slab base 7ft by 6ft which has a viscreen damp proof membrane underneath. This will make it sturdy and provide a bit of "hard standing" for the hutch legs and for us when cleaning out.
This is the plan. Now just need to order the materials and get to it! I intend to let you all know how its going as i progress.
Buns are quite happy in the shed and i let them out for a run as often as i can. Pest control returned yesterday and laid some more traps but they are still empty. I think we might buy one of our own, its just getting the bait that is the problem.
Thankyou everyone.