Count up the sockets in each room and make sure you have enough. I got mine raised up a bit higher than usual and insisted on double sockets everywhere. The height makes them much easier to use.
You should get an outside security light or lights .If getting an alarm, maybe not now but later on, far easier to get it wired in now than later. We got a panic button put into the bedroom when we did get the alarm at very little extra cost.
I don't have them but I believe individual thermostats on each radiator makes for more economy.
If you haven't built yet, make sure the windows you put in are such that allow for easy cleaning.
If they are doing the landscaping , try to be around when its being done to see what sort of soil they are using. If you know nothing about gardening , bring a knowledgeable friend so as to avoid a heap of soil being thrown on top of builders rubble and then levelled. It's important that the site is properly prepared so that the grass will grow in good drainage.
Get some of the attic floored and a light put in . Try to arrange that your floors going in is the last thing that's done......particularly wooden floors.
An agreeable builder with men on site will often do the extra jobs for a lot less than it would cost to bring back someone.As we are hopeless at DIY, we asked our foreman about a lot of the jobs I mentioned and it was so easy rather than doing them ourselves later.
One thing I got was I bought some coat hooks on timber and they put these up in the utility for me. Check also re the height of kitchen counters, particularly if you are very tall or small. Hope that helps.