The coverage of this product is 2-3 m2/litre (75-100 sq.ft./gallon) depending upon porosity and texture of the surface. I hope this helps.

Unfortunately, you cannot place this product over your shingles on a flat roof. Sorry for the inconvenience.

No this product is strictly to keep the moisture out, and does not work as a waterproofer. To prevent water from coming into your basement, you have the following 3 options (of course you would have to dig your foundation):
1) Blue Seal waterproofing membrane which is available in an 18.9 L pail
2) Aquabloc 770-06 liquid membrane, also available in a18.9 L pail
3) Blueskin WP 200 self adhesive waterproofing membrane, which is available in a roll of 36" x 66.7' (must use primer if using this option...Aquatac or Hi-tac)

All of the above products are available at Home Depot.