We looked at going up about 18 months ago. 4 builders all quoted $200K PLUS the cost of what we wanted built upstairs (3 BR's, bathroom and landing area). One of the reasons it was so expensive was because we also wanted to knock out a couple of walls downstairs to open up the back of the house and this would have meant we needed a massive beam across the back of the house to support building upstairs. You can't just remove load bearing walls, especially if you then want to put more weight on top! We also wanted the kitchen and main bathroom reno'd. The cheapest quote (quoted to plans which were professionally drawn) was $298K total. The most expensive was just over $400K.

Needless to say, we devised Plan B and we now have plans drawn up to add a couple of bedrooms out the back! We have done some other stuff - new kitchen, new bathroom, polished the floorboards - and have discovered that it is much cheaper to do things in an 'owner builder' manner than to employ a builder to come in and do the lot.