It comes after Bentley's success with a smaller model car, the Continental GT.
"Over the past 100 years we have made so many different types of cars, there is lots of scope for us, " a Rolls-Royce spokesman said.
He said a longer version of its current Phantom model will be made this year, with a convertible model out in 2007.
Chief executive Ian Robertson was quoted in the Financial Times as saying there was "significant scope for growth" at the firm.
He told the paper the Goodwood site should be capable of producing all Rolls-Royce cars for the "foreseeable future" without having to use BMW plants in Germany.
The company is now thought to be studying the market niche identified by Bentley, which is Rolls-Royce's former sister company and now owned by Volkswagen, and whose GT model has cornered the sub-$200,000 (£105,000) market.
"Obviously Rolls-Royce is not a brand that launches a new car every six months," the spokesman told the BBC.
"We launched the Phantom model in 2003, and this year will be producing a longer version of the car. In two year's time we will be producing our convertible model of the Phantom.
The two-door, four-seat convertible, codenamed RR02, will share the Phantom's 6.75 litre V12 engine and it will be based on the same engineering principles.
"Within the next 12 months we hope to have made a decision about where we are going with new models. But they have not yet been made.
"The Phantom is still the new car in our market and we are concentrating on that at present."