I've done a lot of thinking about this and I will admit my first plan was a little over-ambitious
I've changed the plan slightly so now I'm planning on a timber frame/1/4" gap mesh for the top and front to allow me easy access to the enclosure and for better ventilation,
The sides, floor and back will still be wood I am going to be using MDF 12mm thick and I will be sealing it with Japlac high gloss enamel, I will also use it to cover the mesh, timber and I plan on doing around 3-5 coats to make sure its safe
The sides will keep most of the mess of my walls, the front will be easy enough to keep clean or I could always use some plastic covering
I will be using
THIS rope, to create a few areas for them to climb on and to secure some cork bark tubes, I will be using live plants a couple of the smaller apple trees which will reach 6' max in height(I'll collect the fruit off them because of the seeds in the apples, wouldn't want the gliders getting ill), I will also be planting Callistemon 'Rigidus'- Stiff bottlebrush, Prostanthera sieberi- Australian mint bush but I will let the plants settle, get adjusted and get a decent near fully grown size before letting any gliders lose on them, so they can stand a chance lol!
I still have the same plan for the nest boxes and I will have a couple of larger branches and vines which I will secure to the enclosure
I will have some large pieces of wood on the floor with holes drilled in which I can fill with bugs or gum for them as a little treat, I know gliders prefer to be up high but I thought they still might enjoy it

I will be using a hanging bird feeder for a feeding platform for them which will be hanging from the top, I'll use acrylic to put in the bottom so its easy to keep clean
The bottom and up the sides a little bit will be covered with pond liner, then clay pebbles to absorb excess water, weed membrane over the top and then the bio-active soil and leaves
I will have lots of mesh left over so I'm not sure if to put that on the sides? for them to climb on but I'd be scared of the gliders getting their feet/nails caught

I have worked out an overall price which will be around £850, which isn't too bad compared to the £1700 for the original plan