[chris vickery]

Hi Paul
I built a 30 x 40ft 3 bay garage about 3 years ago and found myself with the same questions. After a bunch of pondering here is what I came up with;

-insulation, really a no brainer. Put as much as you can. I used Fiberglas Pink R-20. Maybe should have opted for R-28 but R-20 works well. An even better option is Roxul. The ceiling had R-50 blown in.

-when I priced out drywall, plastering, finish and paint then compared it to steel sheeting, it came out approximately the same. Drywall susceptible to dampness and damage.

-plywood is very pricey, OSB looks like hell. Plus it needs to be painted and has no fire retardant qualities.

So, in the end, strapped the ceiling and walls. Used G1S fir plywood for the ceiling. Used light grey steel sheeting for the walls. Epoxy painted the floor.
Building is tight, bright, warm and clean. No worries about welding sparks.
Holds constant 15C all through cold North Bay ON winter. Costs me less than
$1000 per year for heating.(propane) Steel is also nice if you own a bunch of magnets, great for hanging things right on the wall.

And to answer the question I know guys will ask, no I don't use a woodstove. A few reasons 1) insurance wouldn't cover me 2) I travel frequently and really don't have the time nor the want to keep a stove stoked 24/7 3) Hard to keep a large space at a constant temp with wood, either too hot or too cold 4) mess 5) potential dangers associated with things in the garage that like to burn eg propane, oxy/acetylene, vehicles with fuel, paint fumes etc etc
One idea I do like is the concept of an outdoor wood furnace with radiant in floor heating. An expensive option to be sure and only good if you're starting from scratch.

Hope this helps