Could I use wood to build 6m quad? If not, what material(s) would be better/more useful?
Bamboo worked fine for me for a 6m full wave loop at 100 watts for mountaintop use in VHF contests.
The bamboo is just sticks in a plus shape and the loop antenna shape will be diamond shaped through holes.
For a single loop, at the bottom of the diamond you need a matching transformer and balun. A quarter wave of rg6 or other 75 ohm coax rolled into an air wound coil will work but won't yield a perfect match.
For a multi loop quad, the impedance will be determined by loop spacing and sizes and can be engineered closer to 50 ohms.