I'm posting this with some trepidation, as I don't know if it's allowed on Mumsnet. I should emphasize I have no connection with the course providers and no financial interest! I just thought these sessions on sustainable building materials (suitable for putting together garden structures?) looked interesting and cheap considering they are full board:
courses.cat.org.uk/sustainable-building/buildingwithstrawbales-detail
courses.cat.org.uk/sustainable-building/sustainable-building-materials-detail