Go back in time and co-found PayPal? That's how Thiel had $1,700 in his Roth at one point, and then a few years later had $28 million. Not an easy experience to replicate.
Even though starting the next Paypal is tough for most of us, what about starting a "normal" company, buying the startup shares in your ROTH (at a super cheap level like Thiel did) and hoping to sell the company down the road???
Even a sale of $500,000-$2 million would make this strategy appealing....Even better if you can start the company and sell it within 5-7 years, and place the proceeds in the broader market to mitigate risk.
A $5 billion Roth is near impossible to achieve, but I think for most of us on this forum, $500,000-$1M is attainable.