built-up roof coating?

go to a roofing supply house. ive been using elastomeric roof paint for years here in Arizona with temps in summer well over 110 degrees. works great, last a long time, years and years, and cuts down on heating cost. but a roofing house would carry the better stuff, and what i buy doesnt cost anywhere near that price. think i pay about $120.00 for 5 gallons. i use elas-tek, number 109 or 114, always put 4 coats, letting it dry one day between. biggest problem people have is not putting enough coats. they say 5 gallons does three coats but if your doing more than 800 square then 8 five gallons will do four coats, and thats putting it on thick. ive seen it on roofs her after 15 years and it still looks good.