I am in the process of installing 2X6s 24" on center on my wall girts - basicy bookcasing it. Then I will use the 23"X93" R19 Kraft faced batts from menards. 2X6s and insulation were bought with the 11% off so that saved a coulple hundred dollars as the two cost about $2K and that is for my 40X64X16. I rough calculated needing 26 of the 133sqft 9 batt packages. I will have a bit left over as that included my walls and doors but then I subtracted two packages as you had to order in qtys of 4s. There are 9 batts in each package. I figured one per wall section so 26 of those then subtracted two pkgs for the two walls with roll up doors.
By the way this is a ton of work and you need to be able to reach all girts the way I am doing it. I own scaffolding, a tractor with pallet forks and have several stacks of ply on pallets that I can roll around with a pallet jack. Keep how to do the work in mind. May be easier to pay your builder to do it day one.
I am doing it this way in order to install these 48X32X3/4 plywood sheets I got as walls. They will be slatwall so I wanted them attached very securely.
Dealing with 8' insulation will be a LOT of work and HEAVY I bet!