I do clean hoods, its my full time gig.
Its all about customer relationships, your hoping to clean their hood for many years. Reoccurring businesses is the best business.
If you clean a dirty hood, take your time, scrape every inch! Scrape the; fan bowl, fan blades, entire stack all the way down, above the filters, the filter tracks, etc. The Chemical is your best friend, it eats away a small layer every time. Apply chemical, rinse and repeat until cleaned. Get on top of the cooking equipment, stick your head behind the filters and inspect, if its not cleaned repeat.
If you can stay ahead of the build up, and rinse light grease, life gets SOOOOO easy! Its much quicker, you get high quality results and happy customers.
Your going to need a pressure washer lance that bends 90 degrees. I built my own, but you can buy one,
Your going to need a razor scraper ~2 inch that has an extendable poll along with many razor blades. you will also need hand razor scrapers.
Plastic! 2mm is about what you can get away with, all you need is 8.7 ft wide. 10 and 12 ft come in handy once in awhile.