Beings this is a new home, do whatever it takes to get the builder to fix the problem. Hopefully, there's a warranty. Start by mailing a certified letter, return-receipt to the builder explaining the problem AND what you've been told so far. This way, if it ends up in court, you have started the paper trail. Document your phone conversations too (date and time and 'substance') so you have more info. Ice damming is a preventable phenomenea. You might want to talk to your Home Insurance company for advice too since they'll be involved at some point (MAYBE). Document that too.
There are products out there to prevent this from occurring. BUT, before you do anything, first read about the causes of ice damming and be sure that whatever measures are taken to 'fix' the problem, ALL the proper measures are taken in your particular situation. (You may or may not have soffits, you may or may not have an insulated roof, etc., etc..) So educate yourself. Here are a couple of links to get you started. There's TONS of info out there on 'ice damming' if you use a WEB Search Engine to find them.
The first link has good info AND a link that talks about preventing ice damming. The 2nd one is more of a product pitch but it tells you what the product(s) do for you. There are more out there so search the WEB.
Ice Damming I and Ice Damming II. Just don't let the builder bully you into this. Pick the right time to say, "I'll be turning this over to my attorney." Give him a chance to fix the problem but again, DOCUMENT phone calls and audit-trail your letters! And one more thing ... Have you had a NEW Home Inspection by an ASHI-approved home inspector?! If not, spend $2-300 to have one. Yes, a new home can be inspected too. Try to find an ASHI inspector and one that is very familiar with doing NEW homes. Since you'll be spending over $100,000 over the next bunch-of-years, spend a few $$$ for some peace of mind.