The average cost per square to install shingles comes down to materials costs and labour costs.
Asphalt shingles are the cheapest per square foot as they sell for $1.50 to $3.5 per.
steel and tile shingles cost between $4 and $7 per sq.
In terms of labor,
you can come up with a rough estimate by multiplying your roof pitch number (usually between 30 and 45)
by the total number of bundles or 10x10 squares of shingles you have,
to get an idea of the actual installation price.
Flashing is always extra as are other water protection measures.
Get at least 3 bids or estimates before you decide on a roofing contractor and make sure they have insurance coverage.