The shed building part will be covered in brief with more emphasis on the climbing wall which I think is the fun part.
For the climbing style it is basically ledges that you can hang on like bouldering (no ropes). On the more solid wood you can even screw some climbing holds to make it easier.
Step 1: Build From Scratch or Retro Fit.
Options for retrofit.
If the existing structure has 2x4 (60mmx70mm)wood structure then you can add a few extra vertical supports, remove the external cladding planks (which can be reused) and add exterior treated structural cladding panels and weatherproofing film etc as per full build.
If your shed has planks that act as both support and actual interior/exterior wall (see photos)then I would leave that in place, build an internal support wall using 2x4 spacing the vertical uprights closer 20 to 30 cm apart to make it easier to screw your climbing planks onto. Alternatively you could make the 2x4 framework and attach to exterior and screw your planks to that.
Step 2: Sketches and Council Approval.
Get it Legal
Before doing anything other than sketching get some info from your local council. The council requirements will help outline your build limits, for us we were limited to height of 3.5m and a roof pitch specific to the area, after a certain size you move to a different set of regulations. We designed it to suit a version of "simple work declaration" which living in France by law the council needed to approve/deny within a month of presenting the plan and paperwork.
If you are going to invest time, money and resources its more ecological to build something that is practical and will last rather than a building that needs to be torn down later.
I had in mind something a little crazy with a slanted roof and polycarbonate roof panels for natural light but local council regs demanded a roof that matched local structures in red tile.
The height and roof pitch made things complicated so I simplified the plan to make a standard style shed. I actually got it through proposing stamped sheet metal that looks like tile and is readily available. The complexity of the tile stamp ridges meant that I had to forget the polycarbonate roof panels. It was just too tricky to get a good joint between the metal panels and the polycarbonate.
I ended up resolving the lighting issue with white paint for the interior and some cheap but bright spotlights 120watt for working on dim days. I also hooked up a motion detector to turn on a 2nd eco (15watt)light circuit automatically when you enter the shed.
Step 3: Tools Essentials
*safety glasses and gloves
Step 4: Safety
The force needed to drill in some screws is quite impressive so keep your spare hand clear if the bit slips of the screw head. I slipped one time whilst screwing a piece of wood and actually pierced my thumbnail, very painful so be careful.
Step 5: The Garden Shed Structure and Foundation.
Why insulate a garden shed?
After a little reading I discovered there was more heat loss coming from the edge of a slab than from underneath. I knew I was going to spend some time, lots of time building it and rather than regret I wanted the option of turning it very quickly into a insulated studio work chalet.
The structure and large A frame roof was prepared in my front car park using chalk lines to set the height and pitch. Then I matched each beam to the chalk lines and screwed the a frame roof. I got a lot of help from my father inlaw a very generous and patient man.
The uprights were mostly recovered beams and traverses as well. At times difficult because they were really old and warped, the traverses were from 1940 build of the house which I recovered from the renovation.
The 4x2 roof wood was new and straight. The walls were framed up with 4x2s were the left over stock with a spacing for 60cm poly insulation panels.
Step 6: Cladding and Water Proofing.
Support wood was then screwed in place so that it lined up in the centers of the framing studs. This is very important so that the wood you will be using as hand holds can be screwed directly through the support wood and construction cladding and directly into the studs.
The support wood allows air to flow behind the final cladding or climbing planks made up of wood scraps available-pine, interior, exterior, palets, planks, beams etc the more varied the easier the handholds.
The breathable film keeps water out of the construction cladding. So if your planks rot or break you can unscrew and replace just that plank.
Step 7: Cladding Puzzle
I used lighter screws for recessed wood that is not supporting a climbers weight. Anything that sticks out would be used as a potential hold so would need to be screwed in place directly into the studs with heavier screws.
I also added new treated pine planks to complete the cladding.
Step 8: Finishing Your Wall
The great thing is that you can add onto or remove climbing planks at any stage even after you have finished the project. This means you can customise the wall for kids or adults. You can even paint coded routes on the planks once you have finished.
You can either keep going right to the top of the roof or leave the climbing section at 2 .5 or 3m and clad the remaining with normal planks.
Step 9: Extra Thrills
A good anchor plate and loop for your rope will be needed.
I would recommend that climbing the this part of structure be done with harness/rope and a partner on "belay" or rope brake.
It is also advisable that you have some sponge mattresses if your wall goes higher than 2 or 3m.
Step 10: Overview
I recycled these materials
*double door closet -slide door
*glass coffee table - window
*wood beams, traverses, trim, planks, chipboard, floor, 2x4 etc
*leftover polyurathane insulation panel
*metal panels from old garage door
*pavers from dump
*Flower pots - lights