Three years ago I moved to a new house. I needed a workshop so I decided to build a timber shed. I was only allowed to build a shed that was 10ftx8ft. I used 3x2 timber for the frame fully insulated on all walls roof and floor with 75mm rockwool and lined internally with 6mm mdf. So far so good. I clad the outside with T&G board as I thought that this would look goo andbe weatherproof. This was a big mistake, after two years the wood had shrunk so much the the joints opened up so much that some of the tongues had popped out of their grooves. On one wall I removed all of the planking and refitted all the planks with the grooves reseated. I had to make a filler plank 40mm wide to take up the gap.
The shed is great, solid, warm and well soun-proofed but I will not use T&G for future sheds.