Welcome Steve. There is a lot of information available here to answer your question. Get familiar with the search feature. There is no set answer to your question as there are lots of different pumps out there. Gas powered, air diaphram or 12 volt. All work, some are better than others. It all depends on the budget and how many roof you plan on doing. for instance if you are going to do 100 or less roofs a year then I would stay with the 12 volt systems. You have a lot of time to read and learn as the season is quickly coming to an end and has for some. Spend the winter reading, learning and prepping for the marketing starting in Feb or March. As far as where to buy I have been dealing with Bob at Pressure Tek for all my equipment and some cleaning supplies.
My name is Steve Spector and I am very new to roof cleaning. What equipment do I buy to do low pressure roof cleaning?
Read first Steve, then decide what roof cleaning setup you want ? It all depends on money. You can start with a delevan 12 volt pump, or move up to a delevan fat boy. Or, you can buy an air compressor and an air diapraghm pump.
Lori from pressure washer products sell ALL the above.
Whatever pump you get, get large diameter hose, we like 5/8 diameter, but 3/4 is a bit better, especially with a 12 volt pump.
We use Kurri Tech hose, and Titan stainless manifold hose reels .