You say, "The slab foundation has cracked." Then you say, "These cracks are in every room in the house." Can you really see the slab in every room in the house?! Do you man the drywall has cracked in every room in the house?!
In either case, you ask the builder for starters. It's normal for a home to settle. If you have a 1 year warranty, find out when it is FINISHED, and ctc the contractor 2 weeks in advance of the Ending Date. Keep a list of problems with the house, including this one. IF you can get away with painting the inside white, make sure you get a gallon of the paint that's being used for painting the repairs later on.
Now, if it's the foundation that's cracked and you don't like the builder's explanation, read your contract. Can you stop construction? Can you get another opinion from the builder's colleagues? YOu can certainly hire a New Home Inspector for a few hundred $$$ just like you hire a Home Inspector for an 'existing' home. They usually inspect the home 1) after the foundation is poured, 2) when it's framed, 3) when it's been plummered and wired, and 4) when it's been finished. (Maybe they do more inspections, maybe less. NEGOTIATE it!) This kind of chump-change is worth it when you're spending hundreds-of-thousands-of-dollars! Don't skimp. I hope you have a Real Estate Attorney for a few hundred $$$ too. THis is where he/she would come in handy too. I suggest you don't hire your friends if you want to keep them. If you have any problems later and they CAN'T be resolved, well, you may lose them as friends. (And tell your friends this too.) Hire an ASHI-Approved Home Inspector. Find out their background too. Negotiate the number of inspections and the reporting you'll get. And don't hire a Divorce Lawyer for your work. You don't hire an airplane mechanic to fix your car, though you might think it's a fair thing to do. Find yourself a lawyer that devels in new home building contracts. They know the business.