Condensation in shed. how can I solve this?

So i built a shed. I insulated the 2x4 walls but did not get to the ceiling yet. It's cool outside and when I warm up the shed via space heater, I get condensation in the insulation and in the rafter beams. I have a few nails sticking through from outside and they bead up and later drip. The siding LP is beading up too on the inside. I put some 1/8 inch wood paneling on the inside and it's getting wet and the screws I used to put it up also beads and gets wet. This condensation is only happening on the sides that doesn't get any sun. I put a sheet metal roof on and that seems to work well. How can I fix this?