If you're redoing your roof and starting from scratch, you'll need to know how many shingles to purchase. There are formulas you can use to determine this.

This app will calculate both normal and unit calculations for a variety of construction projects, including rafters, columns, concrete, stairs, drywall, painting, decking, roof systems, and flooring.

Three recent app releases aim to raise the bar on roof-estimating tools. Two of them are free and modest in function, although one reaches for the stars. The other is pricey and complex by app ...