Where do I input room and board for qualified 529 plan expenses?

If you enter the 1099-Q FIRST, then enter the 1098-T, continue through the interview.

You will get to a "Here's Your Education Summary" screen. 

Select "Other Education Expenses (for all schools)" 

On the screen that asks "Did You Pay for Books or Materials to attend school? 

Room and Board is listed 

The screen is only available if a 1099-Q is first entered. 

You can just not report the 1099-Q, at all, if your student-beneficiary has sufficient educational expenses, including room & board (even if he lives at home) to cover the distribution. When the box 1 amount on form 1099-Q is fully covered by expenses, TurboTax will enter nothing about the 1099-Q on the actual tax forms. But, it will prepare a 1099-Q worksheet for your records. You would still have to do the math to see if there were enough expenses left over for you to claim the tuition credit. You also cannot count expenses that were paid by tax free scholarships. You cannot double dip! 

On form 1099-Q, instructions to the recipient reads: "Nontaxable distributions from CESAs and QTPs are not required to be reported on your income tax return. You must determine the taxability of any distribution."