One of my 2 tier hutches is very thick ply. I painted the whole thing inside and out with really good quality external wood preservative, put smooth roofing felt all round the outside to protect it from the weather and fitted a false roof with a much bigger 8" overhang at the front. It has outlasted several other hutches and is still in really good condition. The only thing I have had to do in the last 10 years is repaint the doors and put on a new false roof last year. I would have another as it is so much better quality than the cheap T&G ones.