His top tax bracket should be roughly 12% feds and 3% state.
So if we postulate that he can save $400 a month starting out, and puts that pretax into the 401K, he saves $400 x 12 months = 4800 + 480 employer contribution = 5280.
If he puts the same money into a ROTH IRA he has to pay taxes on it first so he only saves 400 x 0.85 = $340 a month or less, and saves only $340 x 12 = $4,080 in the first year.
That's a big difference - BUT - saving for a home is a priority for him, and the IRA could be tapped for $10,000 of that.