You don't need much in the way of woodworking skills for this either - you just need know how to nail and screw things together.
NOTE: if you going to make this type of bench make sure your floor and walls are reasonably level, straight and square to each other or you won't be able to swing the legs out evenly.
Step 1: Select Your Wall
Step 2: Build the Legs
Things to watch out for:
1) Make sure the gap at the top of each 'leg' is big enough to accommodate your wall fixing (in my case it was a length of 2x6 timber upon which I hung the bench). The area I mean is shown by the green arrows.
2) Make sure the legs are less than half the width of the bench you have so that they will fold in without obstruction. It's important they're about 4" shorter than half the width of the bench so they've got space to fold out and still be under the bench (not beside it).
3) Also make sure that the width of each 'leg' is of course not more then the depth of your bench or they will stick out the front.
Step 3: Attach the Bench
You can see below how it all went together. I used a large piece of 2x6 to hold the bench to the wall. This needs to be strong as it will bear the weight of the bench when folded down. Also a good idea to attach it firmly. This one is attached to studs in the wall behind the plywood.
Same goes for the legs - make sure they're firmly attached. These are also screwed into a stud inside the wall.
You can see where I skew nailed the rear of the legs in this picture.
I used gate hinges as this will spend most of it's life hanging down and I want it to be well supported. Perhaps this was overkill...
I might add some 'tabs' to the side of the bench at the front in the future just to make sure the legs don't splay out and allow the bench to drop, but they're pretty solid for now and don't move.
All in all this project cost me about £15 as I already had the benchtop. Even if you purchased this I can't see it costing you more than £50 for the entire thing.