Lucky you - your builder has agreed to let you store your belongings and start tiling before you take posession! Most builders refuse this because of the risk of damage or theft. Presumably you have construction stage Insurance but I would imagine that this insurance does not cover your belongings (I'm sure someone here will be able to confirm this). So, as the house is in a construction site, most likely the house is opened at ~8am until 5pm and if security isn't great, anyone can walk in off the street and into your house and perhaps walk away with your belongings! I know I'm playing devils advocate here but it could happen. What if some of the contractors damage your tiles? Also, the builder could fob off some faults on your snag list as damage caused by your contractors? Again, devils advocate but you should be aware. I appreciate if you don't store your belongings in the new house, you'll have to pay for storage but you'll have to calculate the risk yourself. Everyone is nice and pleasant until something goes wrong!
BTW - Best of luck with the new house !