If you are selling this development property, you want to make sure that you get at least 20% on total development cost, the larger the site the higher the ROI needs to be. This does not include your IRR on equity.
If you are leasing the property, you want to make sure that you get 5% of a rental yield.
To determine the return on investment you would need to complete a feasibility study including profit and loss, categorised cash flow and a sensitivity analysis on all aspects of the project costings, income and timing.
Sitting down and thoroughly going through the financial aspect of the project is vitally important to ensure your utilising the best methods to create the best return. Sometimes it might be financially beneficial to actually borrow more and leave your current $$$’s where they are if the return on that is far great than the cost of borrowing.
Also the Tax benefit is something to be discussed and all financial decisions should be planned through your accountant or an organisation that specialises in maximising your return. Don’t listen to the well intended family and friends around you as they most likely send you broke anyway.