Why Not Self-Directed Roth IRA?

Usually when I'm writing here, it's more to share my wisdom (just lobbing that one up there for you to take a swing at) than it is to ask for advice.  This time I'm asking.  I'd love to hear what others have experienced or considered, what holes you see in what I'm thinking, etc.  You could email me at or better yet, I'd love to discuss face to face.

My older son recently started working at Hy Vee, so he'll be able to start an IRA, most likely a Roth.   I've been thinking about how cool it would be if he maxed out his contributions every year, how well off he would be with all those years of contributing and growing it.  But what's a good way to grow it?  I love fixed indexed annuities for conservative growth and/or income in retirement, but he's not even out of his teens.

Here's what I'm thinking I would do if I were in his shoes.  I would max my contributions until I had enough saved to buy a piece of investment real estate (or rather a significant enough down payment that the rent would cover the payments).  Or one of the many other options available for a self-directed IRA.  I'm especially intrigued by the idea of  investing in "intellectual property".  The way I'm looking at things, he could be an entrepreneur who never pays taxes on what he makes from his investments, just keeps reinvesting them.  And then passes them on tax-free if set up as a Roth.  Seems like a heck of a deal.  With a lot of work involved to figure it out.

I'd love to hear your perspective on it.