The reliable way to hire a tradesperson

I had a single story extension built in 2021 and have experienced occasional leaks. We have had the tiler back on advice basis, who has apparently found the odd cracked tile. We are still getting leaks, mainly in line with the velux windows. I have just had an independent builder out to look at it and they have tile me that the tiles that have been fitted are the wrong type, for the pitch of the roof. The tiles are condrun flat tiles (min pitch of 22.5 degrees). Pitch of roof 16.4 degrees. The extension footprint is 8.5 x 3.7 m Do I have any grounds to go back to the builder, given that it was built 5 years ago? Thanks

we were getting damp in the bedroom ceilings. We got some one to remove both chimney stacks. He removed stacks to roof level and put membrane there and re tiled it. Will that cause damp in the future? Do chimneys need air vent?

What is the minimum time to allow for lime mortar to dry etc