Cosmetic surgery, especially breast enlargement, is widespread in image-conscious Venezuela, whose beauty queens have won numerous international pageant titles.
Even a recession has not diminished Venezuelans' appetite for cosmetic surgery with many people taking out loans for the surgery.
Mr Rojas, of the opposition First Justice party, told El Universal newspaper that he was not too worried about the medical details of his offer.
"The raffle is a financing mechanism, nothing else," he told the newspaper. "It's the doctor who will do the operation, not me."
Venezuelans vote on Sept 26 for a new parliament.
The country's president, Hugo Chavez, on Friday denied rumours that he was suffering from cancer.
Local media reports had claimed that the 56-year-old was suffering from cancer in the nasal cavity.
His failure to appear on Wednesday's first day of campaigning for the parliamentary elections fuelled the speculation, although it later transpired that Mr Chavez had been holding a lengthy meeting with his mentor, Fidel Castro, in Cuba.
Mr Chavez, who has inherited Castro's mantle as Latin America's leading critic of the United States, took power in 1999 and plans to run again for the presidency in 2012.