For what it's worth, I recently bought a house. Having a rotating line of credit on a credit card that was paid off did not help with some loan history requirements.

The lender wanted to see loan with fixed payments in the past 3 years (which my wife had, a car loan). Sure, maybe we could have argued, etc. but a credit card paid off each month wasn't a magic bullet for building credit history. I'd say get a nominal loan (not simply a credit card) to build up credit.