You may also want to consider building your own house on purchased/rented land. There are several residential building contractors operating in Sri Lanka some of which are listed below :
Sithagi, Design & Engineering Services (http://srilankabuildingcontractors.com/)
Vajira House Builders (http://www.vajirahouse.info)
Disclaimer: Please note that any third-party service mentioned above is for information purposes only and does not constitute a recommendation by WorkInSriLanka.