Dear Vishwanath
At first in my opinion one should be very clear about the plan of the building/ house to be constructed, the specifications to be used during the construction, knowledge about the requirement of the materials used in construction and finally you or your any trust worthy have time to spent during the construction or not.
If you have detail/ estimated quantity of material and labor than you are in better position to bargin with the contractor to settle the resonable rates and specifications. If you have time than read the gharexpert.com website start construction sub section that will give all answers of your questions and you are be able in better position to make your judgement about your sweet home. Some of links of articles are given below for ready referance.
http://www.gharexpert.com/articles/Start-Construction-1973/Gharexpert-can-save-you-money-during-construction_0.aspx
http://www.gharexpert.com/articles/Start-Construction-1406/Through-rate-contractor;-guidelines-better-rel_0.aspx
http://www.gharexpert.com/Estimator/detailed_cost_estimate.aspx