You can build these on your kitchen table. (just put down 2 layers of corrugated cardboard- I've done it many times- besides, what are tablecloths for ?
Oh- at Home depot, if you don't have a chop saw/compound miter, they will cut your lumber,. have them cut the fence boards in 1/2 for the 3 foot wide ends.
Did you see the pics of the TALL supports? If you want to grow pole beans, peas, cukes, etc (I always grow as much as I can UP, -since slugs don't fly!), then use 2x2 (which is actually 1.5 x 1.5) or those 2x3's, and put on 2 corners on the LONG ends so you can run string. I ran string by tapping little 10 penny nails with BIG heads into the board holding the soil, then made an A frame with tree limbs. String from nail, to top rail of A, back to nail, repeat- zig zagged from one end of ebd to other. Plant beans or peas on string, put lettuce, radishes, spinach UNDER the "A".
BTW- My favorite tool is my Rigid Compound Miter saw,. I bought it for myself as a birthday present when I was single - many years ago.