Roberto ran across the desert, risking death, for the hope of one day living the life of a middle-class American family man.

Three years later, the Mexican-born Roberto is closing in on his dream. He has a steady job at a Las Vegas–area lumberyard. His wife, Anna-Maria, and 6-year-old son have joined him, entering the country on tourist visas. The couple has a new baby girl. And they recently achieved that most American of all dreams: homeownership.

All despite the fact that Roberto and his wife are in this country illegally.

“Brand new baby, brand new house,” Roberto, 31, says with pride in English. His last name is being withheld because of his illegal status.

Immigrants like Roberto, documented and undocumented, are the present and potential future customers for big builders, representing an upward-spiraling $40 billion in annual new-home purchases, an amount that eclipses some of their home countries' entire economies. Already these buyers, eager to achieve what often is impossible for them in their lands of origin, have begun to swell the ranks of first-time, U.S. home buyers. And, assuming no major changes in immigration law and policy, immigrants and their children are poised to become probably the most important home buying group since the baby boomers.

The Joint Center for Housing Studies at Harvard University is now estimating that 1.2 million immigrants have been flowing into the United States each year since 2000, far more than the 800,000 to 1 million the U.S. Census Bureau had projected were arriving. And their numbers have already been felt by sellers of both existing and new homes.

BIG ‘IFS' Immigrants accounted for 37 percent of U.S. household growth between 1995 and 2005, represented 15.5 percent of first-time home buyers, and bought 12.4 percent of new homes, according to the Joint Center. And the group is expected to account for about a third of net household growth in the next decade, the Joint Center has estimated.

What's more is to consider that many of these buyers had to overcome low wages, thin credit histories, and sometimes the lack of a Social Security Number to become homeowners.

Those are challenges their children are less likely to face as they age into the home buying market in the next 10 years to 20 years, just as the baby boomers slow down their home buying. That's when the immigrant effect on the housing market is poised to emerge full-force, taking on an even greater share of the home buying pie because immigrants, on average, have more children than native-born Americans.

“Unquestionably, their children are very significant to the market,” says Eric Belsky, executive director of the Joint Center.