A few years ago (2013) a cowboy builder built a portacabin for my mum. The very first winter the walls were sleeping with damp and pretty much have been since. They refused to sort it and basically muttered something along the lines of "yea some roofs leak". Ridiculous.
Anyway, I'm planning to, if possible, sort it myself so my daughter can use the area as a gymnastics room. It has electricity so heat and light.
My question is, being a complete n00b, where do I start? From these photos, does it look like I need to fix a seal somewhere in the roof? Or outside wall?