The maximum contribution if you hold both is $3000 (soon to be $4000 in a few years, then $5000) - this means that you can also choose when and how to take deductions on contributions, if you choose to, by contributing to either your Roth or your traditional, or half and half. Totally up to you. The normal rules about eligibility concerning MAGI apply.
You and your spouse can contribute a maximum of $6000 (then $8000 and $10,000 when the time comes) a year to separate IRAs.