Collect as many cardboard rolls as possible , no matter what size. Some thing as shown below (Broom packs, aluminum foil rolls etc...)
Then press them so that its easy to cut as shown in the Picture below.
Once you have enough of these cut pieces, either you can colour them with your favorite shades or you can apply wood coats, as done by me for this one.
Think of any simple design and start fixing them the way you want. I tried using fevi-quick but it was not able to hold for long. then I had to try stapling them which worked out good for me.
Once the design is complete and you have stuck every single piece together use small nails to fix them on the wall.