a friendly call to the builder to let him know that everything else is great but there are a few tiles that need fixing (and any other faults) and ask when he thinks the tiler could come and fix them...hopefully he'll respond positively and the problem will be resolved but, immediately after the call send an email confirming what he said and when he said that the tiler would be coming and follow up within the stated time to ask if there's a problem and why can't they fix it to save the bother of getting involved with his insurance company (details should be included in your original contract) hopefully you'll be successful and the tiler will come in between other jobs and do the repair...in the meantime check every single tile (in case there are other hollow ones) and draw a map to identify every suspect tile so that you can check that they're all fixed and, do you have any spare tiles?...have them ready for the tiler or try and identify the tile in case you need to replace any that get broken...only other option is to contact the insurance company and tell them about the builder's response and if all else fails it should be a cheap small job for another tiler and/or you could have a go at fixing them yourself but ask the builder first if he values his reputation and his no claim bonus he'll respond positively

Jut wondering if a builder can build a house with basic structure? And rest i can DIY/ get it does myself by my own contractors?

check with local council if there's some underground sewerage pipes or similar (take your photos and /or ask for their building inspector to check it out...and/or ask a plumber if it may be something related to old sewerage or drainage on the block of land.. we discovered an old well on one property and the solution was to fill the hole with rubble and then we were able to cover it over but dont mess with something until you identify exactly what it is

For the small amount of range hood that would be in contact with the undulating subway tiles, I do not see a problem.