As a ballpark starting figure use around $1800 - 2000 per square metre. This just a ballpark figure to use as as starting point and can easily vary either side. So for $150k for that size dwelling is only around $600 per square metre...... Contact a local designer (the good ones understand budgets and costings) and start from there. Material and product choices will vary the cost to construct greatly so keep that in mind. Building costs are always increasing not going down.

You could always ask the architect the fees, rather than rely on what your friend says about somebody elses's sevices. I would be very surprised if it was 40% extra. I was recently involved with an interstate project where I could not be on-site. A local architect was engaged for the contract administration. The builder had not had an architect involved with the contract administration before. The architect saved the client tens of thousands of dollars as a lot of work was not up to standard, with the builder cutting corners, and substituting materials, which had to be rectified. This included pouring a concrete slab over a neighbours boundary! This appeared to be their standard practice as they were not used to having their work carefully scutinised, and payments withheld, as part of a contract administration process. At the end of the day I don't know if the builder made any profit, but the client did get the building work that they paid for, so received excellent value from the architect's contract administration services. I am sure that lots of people in Houzz who have horror stories of renovations that have developed problems, sometimes due unforeseen circumstances, and have ended up in a confrontational manner with a builder. There are also clients who have unrealistic expectations about the level of finishes that are physically achievable when working with an existing building (which is never square and perfect). If building work goes wrong it can be very expensive, and confrontational. Engaging an architect for contract administration is like an insurance policy and puts a buffer between a builder and client so things stay civil. The architect can work as a third party to administer any changes and variations that invariably creep into the building process in a fair and equal manner to both builder and client. Best of luck, Dr Retro of Dr Retro House Calls

I would like to add a roughly 2.9m x 3.3m bedroom ( these are preferred internal measurements) into an existing rumpus area which is approx 4.2wx 8.0l located on the second story. I will need to allow for a small hallway to allow access to 2 bedrooms already located upstairs. The space I am considering already has a window at approx 1.8 x 2m. It also has built-in storage cupboards across the width of the rumpus room that I will need to remove. Wondering if anyone is able to provide an approx cost and if there are any structural things that may need to be considered. Thanks in advance M

@siriuskey Yes, that's my bad diagram. That end of the passageway has built-in robes facing into each of those bedrooms. There is also an existing storage cupboard across from the WC (it carves off part of the shower space). Ideally we would have a lot more storage, but I'm not sure that it's worth a $400-$500K renovation if we can solve the other issues more affordably! We can put a secure batten door across the carport to securitise it and put a weatherproof storage cupboard in there for camping gear etc. I agree, I like having the separate WC accessible off the alfresco and the laundry tub will be good for drinks!