The method of construction is very straightforward:
Cut four legs out of a log and notch them to fit on to the ends of the bench. I notched these with a small electric chainsaw.
Put arms on top of the legs.
Put a back-rest on top of the arms. I angled the back-rest here a bit. I think it looks nice, but isn't really required. Once you put some screws through the back into it, its not going anywhere. I would have used a large branch for this if I had one.
Put the back on. I attached the back pieces to the back-rest with screws, then put screws up through the seat into them.
I made the coffee table with the cut-offs and some slate mosaic I had left over.
Costs: Nothing - Everything here was either given to me or was left over from other projects.