This instructable will show you how I built my woodshed.
It's made mainly from re-use but need some skills in concrete masonry, arc welding and wood working. Also, some zinc work can be useful for watertightness purposes.

Step 1: Concrete Blocs Base

Our first step will consist in building "feet" for our woodshed. The aim is to glue it strongly to the ground and to avoid ground humidity to damage our logs.

Depending on the size you want your shed to be, consider making 2 or 3 feet.
Mine is 2m long so I made 3 feet separated by 1m

Each foot is made from 2 concrete blocs (50cm long) glued together and to the ground using concrete.
Using a level, make sure that each foot is perfectly horizontal and that all feet are at the same level too.

Step 2: Iron Work

In order to stick the 3 feet together and to allow putting the logs away from ground humidity, an iron frame will be put on top of the concrete blocks.
Depending on your logs length compared to your woodshed deep, you'll need either 2 or 3 iron profiles whose length is the same than the shed width (2m in my case). As my logs are 50cm max and my shed is 1m, I used 3. One for the middle (sorry not shown on the pictures of this step)

You'll also need 4 iron profiles that are basically the same length than your concrete feet. They can be smaller because, in general, it's better if your logs are not put on their full end.

Weld the profiles together as shown on the pictures. Longitudinal profiles have their wing down to ease log stocking while transversal one have their wing up to allow the roof to be fixed to this base.

Step 3: Roof Structure

Roof structure is made from a vertical center support and 2 planks each side to support the roof. In my case side planks come from a huge barrel that explain why they're curved. Straight planks work well too.
Length of these supports will determine :

the roof slope which is important depending on your climatic conditions and the type of cover you put on the roof.
inside volume of your shed. the taller the planks, the bigger the number of logs you can store in it.

First, build center support by making a frame screwing 4 planks in a "U" shape. Fix this support to the base inside the gap between the 2 center transversal profiles.

With center support in place it will be easier to put in place and screw roof supports.
I used a PVC pipe to make a round roof ridge.

Step 4: Roof

Starting by the top (along the PVC pipe), a re-use wood paneling has been nailed to the side supports.

The whole roof has then been "painted" with wood protection (some kind of varnish. Major brand in France is "Xylophene").

Step 5: Watertightness

To make this woodshed waterproof, I used a combination of Shingle and Zinc.

Notes :

Always remember that to be perfectly waterproof, a cover must always be put from bottom to top (reverse of flowing water)
A special glue is used for gluing shingles, It looks almost like tar (or asphalt)
Cover nails are special nails that are zinc plated and have a very large head. Use them to avoid leaks.

First, a zinc strip longitudinally folded at 90° is nailed on the paneling to fill the gaps between the wall and the shed.

Another zinc strip covers paneling edge in the front of the shed to protect it from rain.

Then shingle is nailed and glued to the roof from bottom to top.

To finish, a large plate of zinc is glued on the roof ridge PVC pipe and glued / nailed to the roof.