If you have a larger sized lot, and your Zoning and R-Codes are favourable, investing in a multi-unit development could be very rewarding. Multi-unit sites (including quadruplex sites) are generally a more complex project than a house behind a house, duplex or triplex development because the local council is required to consider a range of additional factors. The costs are higher and the build time longer, so make sure you have a strong business case and that your timing accounts for a longer wait before the "pay day". Ensure you get the title structure right too, or you could wait longer than you planned for settlement. Paragon Homes WA has the requisite experience in building multi-unit developments, so we can definitely help.