We are looking to buy a PPOR property - the lot has approved plans and permits for a two-lot subdivision. Its basically fixing and extending the period home in front and building a townhouse at the back. The already have power and sewerage already connected to the back lot. We don't have any experience with building - and looking for community's guidance on what steps we need to take to best estimate the build costs. The existing owner engaged the architect to create the plan to extend and fix the period home in front and squeeze a townhouse at the back. The plan looks good to us, but doesn't have any renders included. From my reading so far, anything involving customised architect plans for extending could be very expensive. My questions: I will ring a few local builders to ask for a quote. But would they review the architect plans and provide estimates as it is ? How reliable are those (As these won't be quotes). Based on that cost, we will make a decision to buy or not to buy. Lets say we plan to buy this. I presume the next steps is to get the Building Approval ? What are things we need to see to make sure we don't have problems with that. How long generally this process takes ? When does the actual subdivision takes place ? Post building approval, pre build ? (As post subdivision, there will be two different addresses) How does the mortgage process works in this case ? We first ask bank 80% of current purchase price. Then do subdivision and building approval and then ask for 80% of build cost ? Last question. Assuming we can afford it - can we buy the house, work on the front renovation and then build the townhouse at the back later stage (I assume approvals don't expire)? Apologies upfront for noob questions. Doing a lot of reading on this subject but wanted to confirm all this.