There will be people on here who have probably made hundreds but for me the easiest way was a pair of sash clamps and a set square. Quick and easy that way and just personal preference I use gorilla wood glue for anything like this, good applicator built in and seems a little thicker when applied.I’ve got to start assembling mine - need a set square for the right angle and some outside wood glue before starting to assemble this week after work. Also ordered another 10 brood frames and foundation so have 20 plus the end board for 9 spare - so plenty to be getting on with.