This one is made of surplus pieces of hardboard + tie-wraps, but the concept can be used with many (scrap) materials.
Step 1: Get Your Materials
This way you can make a form-fixed structure without the need for sturdy joints.
What you need are three basic things:
Sheet material. Use whatever you like as long as it's strong enough for your needs. I used 3mm hardboard because i had a lot of it left. It bends when you put weight on it but it doesn't break easily.
Corner connections. Tie-wraps is definitely an easy option, but wire or rope will also do the trick.
Wall connections. Screws with a washer or something like that so you can connect a tie-wrap to it. I found some old meccano corners that were really handy for this.
Step 2: Measure
If you use bendable material like I did, don't make the shelves to long. Make your corners so that they give good support. A 90 degree corner is best, but you can make it a little more or less to make a nice shape.
The best method is to make a sketch, and then mark out the corner points on the wall. Once you have these you can measure the distance in between them. Write the measurements in your drawing.
By the way, you don't need to be super-precise. If you make a little error the shelves will still fit because not all the corners are connected to the wall.
Step 3: Prepare the Shelves
Then drill three holes in the sides for the tie-wraps. It's handy to make a little drill-template if you need to drill a lot of pieces.
Step 4: Screw
Choose it so that the upper corners of vertical shelves have screws. These are the corners that will be pulled on so they need some wall support. The lower corners will only press against the wall.
Step 5: Bind Everything Together