I've always like making these Viking or stargazer chairs; it's a simple furniture project that doesn't take long, doesn't need serious skill and gives an excellent result when it's done. I've been thinking a while though about the fact that you need boards that are 12 inches wide or so ideally and the fact that good boards this wide aren't cheap.
By laying and gluing the pallets on top of each other and applying pressure, I've ended up with these substantial slabs of timber which are ideal for this purpose. The nail gun is a great help, but a regular hammer will be alright.
I'll start with the 'T' piece, the seat is about 11 inches wide or whatever the width of your boards, depth is around 12 inches. You'll cut the tongue, so it's 7 inches wide, the cut near the seat needs to be angled, if you just do a 90-degree slot, it won't be as comfortable.
The back piece is simple enough; I'm a fan of gothic arches, so I do a gothic arch, curved or straight also works well. Cut the slot about 11 inched up from the body, 7 inches with and at a 70-degree angle, experiment with drawings and holding the wood on top of each other, so you get a mental image of how it looks together.
You've almost did it, you've got a working chair, what you do to it know is down to you. I'm a big fan of Lichtenberg and glow in the dark so that's what I do to them, go mad and put your spin on them!