Just thought I would mention it is worth talking to your builder and seeing if you can negotiate payment / settlement on completion.
Not all builders will allow this (particularly not the smaller companies) and it does cost a bit more (Added 10k to the IP we are building, plus extra stamp duty), but gives you more flexibility. By paying on completion, the builder covers all the costs throughout construction and you just need a normal home loan for settlement (like you would if your were buying an established house). So there are no repayments until after you have settled.