Travel and other expenses are treated as additional gambling losses, and are subject to the same rule. Your total losses, including expenses, cannot exceed your winnings. As a professional gambler you cannot show a net loss on Schedule C. The most the expenses can do is reduce your net gambling income to zero.
(The law on expenses was changed starting in 2018.)
Note that you have conflicting goals in trying to be able to make a Roth IRA contribution. In order to contribute to a Roth IRA you have to have "compensation," and the amount you can contribute is limited to the amount of your compensation. A net profit on Schedule C is considered compensation, but if your losses and expenses reduce the net to zero or very little, then that doesn't give you the compensation that you need in order to make a Roth IRA contribution. And if you have significant other compensation, such as from a job, claiming to be a professional gambler is questionable.
