There are many
disadvantages. Fact is 75% of home buyers would
avoid buying any new home built after 2003. Number one, has to be poor quality and indifference of housebuilders to fulfil their warranty obligations.
It is often the case that new homes need
more work after moving in than a well-maintained 25 year old house.
The "help" of Help to Buy is no help at all as housebuilders have inflated prices way above the 20% help. If you add in legal fees and the lost equity increases of the 20% you don't own over the 5 year interest free period, using Help to Buy for a new home does not make any sense at all. All it has done has enabled people who cannot save a deposit, buy a new home at a higher prices, that they cannot really afford.
As with everything, one person's opinion will differ from another. But the main thing to consider is, who will buy your second-hand small, dark, home when you decide to move?
It will probably have a very small overlooked rear garden, no front garden, with ongoing management charges for non-adopted roads and public open spaces, on a run down estate amongst social housing peppered amongst owner-occupiers.
At least you can see an existing house, negotiate on the price and get a full structural survey before you buy it! None of this is possible with a new home.