Presume BGM means Big Green Machine. Record?
I also have a concrete sectional garage for a workshop. The best thing I ever did was replace the asbestos type roof with twin wall polycarbonate. To counteract the crazy heat of summer I have moveable sheets of 3mm, 4' x 2' ply. Not quite big enough to fully cover the inside - leaves about 6" at the ridge uncovered, but that gives a lot of extra daylight.
Other changes included increasing the pitch of the roof to gain extra storage, by making new 'A' frames out of unistrut (because it was free) but angle iron would be suitable. There's not really a lot of weight to the original roof even when covered in snow as it's evenly distributed. The original 3/4" (Edit: 1") angle iron 'A' frames would easily stand my weight.
Because I had to make new apex end panels to accommodate the change in pitch, I made one end slide outwards on four 20mm x 8" (Edit: more like 12") lengths of galv conduit (again free). That also makes a huge difference in summer.
I haven't bothered with wall insulation because of the space it takes up. In winter I have a small 5kw wood burner which keeps the place warm, sometimes too warm & I have to open the door. Previously I had a wood burner made from a gas bottle that also worked quite well.
Shower curtains & roller blinds are also a good idea - had them for years. Also have roller blinds on the front of shelving units to save them becoming filled with dust.