Question 1049601
area of each wall is {{{12*24=240}}} square feet.
area of four walls together is {{{240 + 240 + 240 + 240 = 960}}} square feet.
two coats on each wall would be similar of painting {{{960*2=1920}}} square feet.
area of roof is {{{10*10=100}}} square feet (double coat on roof is not mentioned).
area of each wall with two coats + area of roof with a single coat = {{{1920+100=2020}}}.

A gallon of paint can cover {{{512}}} square feet so, four gallons of paint would be needed to cover {{{512*4=2048}}} square feet.
paint which can cover {{{2048-2020=28}}} square feet will be left.