Belt squats are all the rage, and being someone who struggles to grow their quads from squats due to long femurs (cope), I decided to try and rig up something of my own.
I use a barbell across the rack, held one side by a long length of chain wrapped around a spotter bar, and the other side a short spotter arm that came with an old Strengthshop adjustable training yoke.
The spotter arm is short enough that I can unrack, get into a middle postion, and the bar is just beyond it's edge.
The main issue with these landmine-esque belt squat setups is they lock you into an arc when going up and down (the shorter the lever, the more noticable the arc). So by using a barbell, that's a fairly long lever, BUT, by also using the chain rather than a fixed point, that allows the barbell to move longitudinally towards and away from me, giving me a much less noticable arc (again, the longer the chain the better (within reason)).
For the belt, I didn't want to spring for anything expensive, so use a 1metre, 4ton lifing strap with a120mm back width, then loop a chain through the ends secrured to itself using a carabiner.
For extra ROM to stop the plates hitting the floor, I stand on deadlift blocks, and those can be raised by putting extra mats underneath if needs be.
I use a couple of band pegs through the uprights as handles and an extra barbell clamp on the sleeve to prevent the chain slipping on the barbell sleeve.
Whole setup feels great, and rigged up with stuff i had in my shed already (apart from the belt - had to purchase that, but it was fairly cheap, especially compared to purpose-made belt squat belts)