Re:
I have finished the outside now. Apart from the trim around the roof.
I am now installing the cables for sockets and lights.
Regarding waterproofing the cladding and roof seem adequate.
For the roof I used wooden boards, then covered the boards with a layer of plastic sheeting, then finished off with the wooden shingles.
Once I have installed the wiring I will be insulating then cladding the inside.
Very much enjoyed building this summer house, considering it was my very 1st attempt.