As you can tell by the date I joined the forum, we've been thinking about this for a lonnnngggg time. I must be honest and admit that I forgot about the forum but then rediscovered it about 3 months ago and have been lurking ever since - I love Modernisation of an old girl - gorgeous job
In fact I initially had plans drawn up when we first moved into the house 9 years ago (for a much smaller extension I might add). The new addition is 310m (including garage, verandahs and alfresco)
The initial amount the estimator estimtated (is there such a word) was $282,000. Having said that this did not include the designers fees and extra survey required, some solar power just other things that seem to go wrong. Also does not include Pool and landscaping but for some bizare reason does include the glass pool fence!
We did not go into owner builder thinking we could do it cheaper - we were hoping for a better job (home builders apparently being pedantic and flexability.....I haven't even thought about tiling etc yet)
I havent regretted doing it (so far) but I did underestimate the time it would take (we are lucky and live on site and have our own business 5kms away - I don't know how you would manage doing it working full time in the city and have to go to site every day and then home. The other piece of advice I am going to give is that your designer/ draftsman/architect are really important and trying to save a couple of $$$ here may cost you big time later on. I wish we had done more research on our designer .....khe sara.
Last bit - live with your plans read your plans - give your plans to other people to read because if you are anything like us you will see the things on the plans that you expect to see (kind of like how you can read a word if you have the last and first letter and the right number of letters) you wont see what is actually there.
This is what our house looked like before we commenced
The pool that was demolished
A rough idea of our plans