Hi Silver,
Per your reply #34, two (2) very major heating concerns:
1. You say you have roof ridge vents every five feet. If these vents remain open in winter, & are "not" sealed, they can allow more heat to leave the building than that of open wall openings because heat can rise up the sloping roof & cause a draft & negative pressure inside the building ...... then cold air is drawn into the building through every crack & crevice in walls, openings, & unsealed roof eaves & rakes. (Similar to having central heat in a house with an unlit fireplace with no damper -- the chimney it will suck out heat like an electric powered roof vent).
2. The metal roof has about the same insulation value as a canvas tent. Had several experiences with GP Medium Army "Warm-Up" tents in the winter of 1966, which were heated with two (2) diesel fuel type Army field stoves with smoke stacks. At minus 15 degrees outside, & a strong wind, medics measured the inside of the tent & found it to be plus 20 degrees with 30 soldiers standing in the "Warm-Up" tent ............. even with black chimney smoke that could be seen for miles.
If you decide to have insulation placed immediately under the metal roof, (thickness depending on rafter depth or purlin depth), it can be supported on poultry wire, followed by a metal building type vapor barrier stapled below if the above roof structure is wood.
If you omit the vapor barrier, warm moist interior air will definitely condensate on the underside of the very cold metal roof, but only in cooler outside weather.
With no vapor barrier, roof insulation will get wet in winter from above & drip water which will resemble roof leaks.
If wanting to insulate, please get a group of young guys & as you say, stay away from ladders ............. try calling several metal building companies to get several names of metal building insulators, & get estimates to provide same.
Energy consultants are just finding out what I learned & constantly practiced since over 40 years ago; i.e., it is much wiser to insulate roofs in lieu of ceilings -- e. g,, why have a 150 degree attic in summer & a 20 degree attic in winter with heating ducts & air conditioning ducts running through extreme high heat & frigid cold.
Sincerely hope this helps if you try to get estimates to insulate your shop.
If other questions or problems, lots of different opinions here.