The standard rule is the price of materials times 3. But that's for a whole job. Sheathing, felt paper and shingles. So before you make your bid, go look at the job. Determine if it is a full rip out and replace or just an overlay. Once you have your measurements for a full job, base your bid on the materials and the labor keeping the rule in mind. You are usually ok if you stay close to that figure.
For just an overlay the average price is between $120 - $150 per square. That is North Carolina prices. It may be lower or higher in your area.
Hope this helps you out, if so please accept. Please contact if you have more questions on this.