correct sealant?

Roll of plain felt not shed quality thin stuff.
Roll of mineral green or whatever.
Mastic adhesive.
Random clout nail the first sheet/s on starting from the bottom over lap each sheet going up 3ins
the mineral (top layer) lay first sheet allow 2inch overlap at bottom and sides. place the sheet with overlap strip up the roof tack with clouts along over lap strip mastic along the over lap strip and then apply second layer again with the over lap strip up the roof. If pent (single slope) over lap at top again 2 ins randome nail all the edges folidng in the corners. If pitched roof (slope each side) apply capping piece on top random clout nail and coat nails with bitumen adhesive, nail edges to eaves and barge boards on sides of the pitch.
Just done mine. Done this way it will last years and the shed will fall down before it leaks.

Bob
September 2010