Worse problem after my house build was my windows. I had wooden ones fitted but they leaked like sieves from day one. Probably worse than sieves. When the glass was fitted they never sealed the bloody things. Within a year of my build I had to remove them and replace with uPVC.
With regards to the roof I was told by another farang to put in a rubberized membrane under the tiles. That was good advice but the builders found it difficult to install because they couldn't attach it to the metal laths. I had to bodge repair any leaks as and when myself. All dry now.