Old house with wood shake shingles may have only wood stripes

with gaps between them on rafters. You have to cover with 4x8 sheets of plywood before put in felt paper and shingle.

I just guess your roof is 20 squares. Material shingles + felt paper...  $2500. With tear off and disposal for $8k it doesn't make much money.

20 square needs 80 sheets of plywood. If it is a high pitched roof, it is difficult to handle these 4 ft by 8ft pieces 30 ft from ground, making cuts, and nail in one next to another. I would say crew of 3 for 4 days minimum.