Measure the distance across the roof from one edge to the other, and cut a piece of roofing felt to this length, plus an inch. Lay the felt down on the roof so it sits centered, with 1/2 inch hanging off each edge, and ½ inch hanging off the eave as well. Staple the felt to the roof every 6 inches around the edges.
Place the first starter strip shingle at one end of the roof eave. Leave 1/2 inch of the starter strip hanging off the roof edge and 1/2 inch of the starter strip hanging over the eave. Mark the edges of the strip where it touches the roofing felt with chalk.
Pull the starter strip shingle up from the roof. Apply roofing cement to the back and press it down into place so it lines up with the marks on the roof. Nail the starter strip at the two top corners and at the vertical center of the strip, just above the line that runs across the strip on both edges.
Lay the next starter strip shingle so the edge lines up with the side edge of the first strip and the bottom hangs off the eave by ½ inch. Mark the top edge of the shingle on the felt, remove the felt, cover the back in roofing cement and secure the strip with nails. Continue across the eave in this method, then move to the eave on the other side of the roof.
Install any types of Roser roofing over the starter strips. When installing the first row of Roser roofing, place the roofing so the shingles cover the seams in the starter strip row.