Dear Ram
For an estimate to find the cost, There are two ways one is detail estimate in which the estimate is framed on the basis of plan of the house, elevation and specification used in construction of the house and this estimate gives you the accurate cost and quantity of different type of materials used at site.
The other method is tentative cost i.e. rough cost estimate. for calculation of cost by this method you can use gharexpert.com ESTIMATOR in this mehod place area and specifation and you get the cost.Link of estimator is given below.
http://www.gharexpert.com/Estimator/Startpage.aspx