Depending on the type of develop you wish to do, you may want to use the equity you have currently, or borrow from a lender. If the latter, you must consider that the interest will be higher than a typical home loan.
Ensure you are crystal clear on what the builder is providing in the contract as to minimise the cost of variations during the project. If the build contract isn’t made clear, you could be caught out fronting the expense of the costly variations.
Identifying who your target audience is in the current market is extremely important. Knowing what type of people they are (singles, young couples, families, elderly etc) and what their values are become paramount if you are wanting to give yourself the best sales opportunities possible.