The best thing when choosing a tradesman is personal recommendation and see if you can get out to view previous work local to you if it's on a roof especially (so you don't need access to go into anyone's house) - if not, try to get pictures and critically assess their work, because review sites aren't worth much these days. Some don't let you leave negative reviews and a lot of reviews are paid for (my previous company paid the workers bonuses for leaving google reviews for their own work!)
Modules are supposed to be supported on the roof and then the tile/slate should be dressed in around it appropriately depending on what sort of install you've got.
Drilling straight through slate means you're going to have leaks, 100%.
Modules are supposed to be supported on the roof and then the tile/slate should be dressed in around it appropriately depending on what sort of install you've got.
Drilling straight through slate means you're going to have leaks, 100%.