Had a small extension built with a new roof done in marley type interlocking tiles. When it pours ( as happens occasionally in Glasgow ) the rain water flows straight over guttering directly onto decking. The guttering is 115mm wide with the tiles overhanging between 75-85mm leaving only 30-40mm to outside edge of guttering. The builder is coming back next Thursday to sort some small snags and would appreciate any advice on how the builder should go about fixing this properly, I'm assuming this has not been installed correctly?