Putting up the lean to off the shed. First when it's done should I put a vapor barrier down before I lay down my base of gravel under it. And second should I get that bubble wrap insulation for between the perlings and metal roof to discourage condensation. I have that in my shed and no condensation at all but do you need that stuff for a lean to with so much ventilation already? I mean a little drip here and there is no big deal but if it's like it's raining under there I might as well not even build it.
My thoughts would be that putting the insulation would be over kill. Condensation shouldn't be and issue, it will have plenty of cross ventilation.
Throw down some large gravel and you should be fine. Unless the floor area is always wet and will pump, you should not need road fabric.