While we have some non-USA members, I'm not sure there's anyone here that can give you any ideas about costs in the UK (assuming you mean that London). Building a house gives you the opportunity to make it the way you want. But, especially if it is your first house, sometimes what you think you want isn't what you really want until you've lived with it. So, some people wait and move a few times before they get a good handle on what works for them and what they really want before building. Remodeling gets MUCH more expensive if you decide you want to change the general layout of the house...it costs to tear it apart, and then it costs to build it back up again. On new, depending on what you're doing, it may be cheaper; depends on how much of an old structure you decide to keep.