The gharexpert website give us lot of information about the construction of building, specification of materials, how to hire contractor, payment schedule and detail cost estimate so that contractor can not befool us if we know all the things before giving a contract to the contractor. I generally feel we people have more trust on the mason and contractor than the qualified civil engineers and think that a small amount given for structural design and estimate etc is unnecessary but after starting unplanned work spent huge extra amount to complete the work. If you read the construction section i.e. Start construction than find lot of information. For contract you should go through the article link below http://www.gharexpert.com/articles/Start-Construction-1406/Through-rate-contractor;-guidelines-better-rel_0.aspxNow handle the contractor tactfully and give money I.e. actually required to complete the slab work by taking a detail from him i.e. cost of cement, steel, shuttering etc and supervise more vigilantly and ask him now make payment schedule for rest of the work. Pay him tightly.