When coverage is difficult to estimate, add more rather than less. You can always pour the leftover back into cans. For large jobs, use the bucket and a roller screen rather than a roller tray. It’s much faster to load your roller with the screen than to use a roller pan. Simply dunk the roller into the paint bucket, then roll it along the screen until it stops dripping.
Homeowners painting their home, whether it's a new coat or a new house, should ask their contractor about low-emitting paints. As the paint is applied and dries, it can release high levels of VOC's, chemicals that may be toxic to the air your family breathes (not to mention, they stink!). On top of that, these off-gassing chemicals can be absorbed by soft materials already in your home (carpet, furniture, pillow, fabric) and act as a new source to continue releasing harmful chemicals (known as "the sink effect"). There are tons of third party certified low-emitting paints on the market now for more competitive pricing and selection. You can find them listed on my organization's website at greenguard.org (those that we certify) or you can find more info from your contractor :) Happy painting!
The cost of paint is about 15-25% of the cost of the contract. Mid grade paint costs about $40 per gallon with contractor pricing. If you are painting your home for real estate purposes and you don’t want to spend a lot of money, there is cheaper paint available. Stay away from anything that costs less than $25, you are buying watered down colour that is difficult to use. If you are thinking of using the most expensive paint available, you can spent over $120 per gallon from manufacturers like Farrow & Ball. Whatever you decide, keep in mind that since labour is your biggest expense, why not use the best paint your budget will allow.