If I missed anything you found from your build, please comment on this page!
It's not the deal, it's the overall cost that counts
Try to imagine how you will use the houseOur lighting plan was pretty good, but there were some things I had to ask for, like a switch at both ends of the family room for the lights. Some builders don't double switch the hallway light, so you spend your life shuffling back and forth between the switches. You may like to have a switch for the bedroom light next to the bed (or have pendant lights instead of bedside tables). Will your favourite furniture fit against that wall? Consider the location of the hot water service in relation to the tap that you really don't want to wait for hot water from.
Lights are part of colour selection tooThis is one of our regrets. We changed from down-lights to pendants, battens, or fan lights in some of the rooms where we wanted the lighting to have a bit more character, which is fine. But we didn't go to the lighting store to find our lights until after the contract was final, so now that we have the lights, we want to modify the lighting configuration a bit - but we can't change it now without incurring a penalty cost for making changes, so we will wait until after handover and change it ourselves. Another thing to consider with lighting is that there is a new building regulation that requires a maximum of 5 Watts of lighting per Square meter in the house.
Don't be afraid to walk away
I am told it is common for people to conduct negotiations with multiple builders at the same time. It's a difficult decision to make and sometimes you don't have all the information until you are a good way through the process. We walked away from two builders who we weren't comfortable with, and now we couldn't be happier. Had we continued it may have still been ok, but personally I don't think building a house should make you feel uncomfortable... paying for the house, now that's another matter.