You're gonna need way more than 30K.
To get the kind of money you'll need, you have to leverage your individual skill-sets into something that makes you money fast.
Build a relationship with a small bank, sell that house you just built and use the leverage of that money to build two entry level spec duplex homes. Then do it again with three. There's a very strong market out there right now for that and I don't see it abating for several years going forward. You won't be stuck sitting on something that won't sell. If you're in Chicago, buy distressed lots in urban areas preferably without an existing structure, ie the demolition has already taken place. You obviously know enough tradesmen to get the work done at reasonable rates. Minimize the actual work you do personally. While it might save you money, you'll make it up in quick turnovers of your capital. Key here is finding the right bank. By the time you're 32, you'll have enough money to trade full-time and still build homes. It sounds like you have what it takes to do both.
Edit: lol... I just read the previous two posts that went up while I was typing this one. There ya go.