The shingles needed to be replaced because they're rotten. This
is not really a specialised job but we feel it's not a DIY job
either. It's a bit tricky and frankly not an enjoyable one. When it
comes to replacing your shingles there are two options, pine and
cedar. I've gone for second grade 2 Cedar it is the cheaper option,
but we are going to paint it.
Carefully remove rotten shingles starting from the top and working your way down.
Take note of the pattern and spacing of original shingles. Your new shingles need to go back exactly the same way.
Remove rotten plywood (which is under the shingles) if needed and replace with building paper and new plywood. You can just cut out the rot if all of the plywood does not need replacing.
Check framework for rot, replace studs, plates or batons if
Once all is back in good condition (sound state) start to fit new shingles from bottom to top this time. Use a string line to keep a straight and level edge.
I set the corners up first building them up like a pyramid, once you have the pyramid set up, you can then set everything else from that pyramid. The better you start out here the better the job will come out.
Shingles provide their weatherproof qualities by overlapping each join. A double layer at the bottom makes them doubly watertight.