What are the manufacturer warranty prices for the low slope roof systems you install?
Anywhere from 3 cents psf for a 10 yr commodity to 20 cents for a 20 yr green roof.
As with any insurance, it's all over the board, dependent on what particular "manufacture", & whether the warranty covers material only, material & labor, specific time length, depreciated structured, dollar limitted, or "NDL", (No Dollar Limit), minimum premiums to per-square fees, etc....A simple call or website search to the particular mamnuf.; One can determine.