BEND, Ore. (CNN/Money) – Joshua Carlson was just an undergraduate business major at the University of Minnesota when he set his sights on his first real estate investment: a duplex he and a friend were renting near campus in Minneapolis.

"It was the perfect set up," said Carlson, 31. "I knew I wasn't going anywhere for a while, and I knew my neighbors didn't want to go anywhere for a long time, either."

Joshua Carlson

Though the building wasn't for sale, Carlson started talking to his landlord about the possibility of buying it. Eventually, they struck a deal.

With a $5,000 down payment and financing through his landlord, Carlson bought the building for $105,000 shortly after finishing his undergraduate degree. Carlson paid his landlord 8.5 percent interest on a 30-year loan he could pay off any time, which he did when he refinanced two years later.

"That guy really helped me out," said Carlson of his former landlord. Now, the duplex is worth three times what he paid for it, according to a recent appraisal.

By day, Carlson works as a technology consultant earning between $80,000 and $100,000 a year. By night, he is in his second year at William Mitchell School of Law, where he is focusing on real estate law.

In November, Carlson will close on his fifth property, bringing his real estate portfolio to about $1.75 million. He estimates his equity portion is about $600,000.

Buying real estate was a natural progression for Carlson. He started mowing lawns in grade school and paid his way through college working at a public golf course in the summer and at an ice rink – as a Zamboni driver – in the winter.

"My brother used to call me Alex P. Keaton," he said, referring to Michael J. Fox's financially astute character on "Family Ties."

In 1998, Carlson bought a second duplex on the same block as his first unit. This building was also not for sale, but Carlson searched the county's property information and tracked down the owners.

"I sent them a letter and they responded favorably," said Carlson, who negotiated another contract for deed for $110,000 until he could refinance at a lower rate.

In 2000 Carlson, tapped his savings to buy a third duplex, and in 2002 he bought a fourth one, which is where he lives now.

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"The common theme to all of the properties is they're in nice neighborhoods and they're within two blocks of water," said Carlson, who also contributes twice monthly to an investment account worth about $70,000.

He favors older Minneapolis neighborhoods over the suburbs because he knows those areas well, and he thinks rental demand is strong in them.

"The only vacancy I've had in all of this time is about two to three months," said Carlson, whose tenants are primarily graduate students at the university. He rarely advertises for his apartments. Instead, he depends on recommendations from his existing renters.

Carlson's total cost for the four properties is about $7,600 a month, including mortgage payments, property taxes, homeowners insurance and routine maintenance. Meanwhile, he collects $7,800 a month in rent and lives "rent" free.

"I don't really care about year-to-year fluctuations (in the real estate market) as long as the rents pay the mortgage," said Carlson. His goal is to accumulate as much property as possible, pay it off within the next 25 years and live off of the rent. "Even if the property doesn't appreciate, you still have income."

In November, Carlson will close on a new condominium in downtown Minneapolis, which he and a friend agreed to buy for $166,000 three years ago when the project was speculative. The price of condos in the building has gone up about 10 percent a year, according to Carlson.

When he graduates from law school in late 2005, Carlson hopes to trade his consulting job for one that focuses almost exclusively on real estate.

Meanwhile, he wants to buy a larger apartment building using a 1031 exchange, which is a tax maneuver that would allow him to trade his duplex for another building but avoid paying capital gains taxes.

"I'm trying to find a mentor who can help me take the next step," said Carlson. "I don't need someone to hold my hand but it would be nice to work with someone who's already done what I'm trying to do."

Sounds like a job for Donald Trump. Producers of "The Apprentice 2" are auditioning candidates for next season's cut-throat reality show at this very moment.