Hi Ruthirama - I'm not a contractor, but if you are looking at quick rough numbers, of course you start with the purchase price of your property. To scrape a lot, figure $40-60k, so say $50,000. Building costs can range from below $200 per sq ft to well over $400 per sq ft, depending on quality of fixtures, finishes, and craftmanship. So, based on your question, costs could range from the low $400k's to almost $900k, plus the cost of the property. As usual, the devil is in the details. I would figure out if your budget was within this range and then get together with an archetect and/or contractor to come up with the optimum plan to fit your budget. To determine your budget, work with a reputable lender to secure financing before you waste any time working on a plan that can't succeed.