We have alot of old pallet racks for sale at work. COuld a person use
the verticle sections as posts and the supports as girts in a pole
barn constuction. I am really needing a detached garage to park my
cars in on the cheap. I would use regular plywood on top of that then
siding to match the house.

Where you live is there
1. Code inspection, Homeowners Association restricions, required
building permits, or other government control for outbuildings?
2. Snow or wind load?
...if you can answer "no" to both of these, you might be OK. Do a
search
on "free barn plans", and you'll find a bunch of .edu websites with
plans
for barns, sheds, outbuildings, etc. including the trusses.

Personally, I'd be tempted to make the structure big enough so that I
could use the rack shelving as rack shelving on either side and still
get vehicles inside (dunno if you're planning 1 or 2 car, etc.). It'd
be wicked easy at that point to add benches, etc. Since the posts are
likely set up for it, I'd either do a slab-and-sill, or at least
sonotubes, with J-bolts to mount the posts.

If you can get it cheap and get/avoid permission, it sounds like it'd
make an excellent garage...
--Glenn Lyford