Is financing possible? Building savings contract or savings book?

Hello everyone,

my girlfriend and I are currently living in an apartment with my parents.
We don’t have to pay any rent there monthly.

We plan to build a house in about 3-4 years.

My girlfriend will start working on 10.01.2011.

She will earn about 1200 net in the first half year, and about 1400 net after the first year.

I currently earn 1800 net.

Together we would then have 3200 euros net.

I am currently paying into a 70,000 [er Bausparvertrag]. By the end of 2012, about 28,000 will have been paid in, so it can then be assigned.

We are now considering whether my girlfriend should also start a [Bausparvertrag] now or pay monthly into a savings account.
I think some cash can’t hurt when building a house, but of course a [Bausparvertrag] also has its advantages. However, we want to build in about 3-4 years.
I don’t know if you can save that much in a [Bausparvertrag] by then.
I would be grateful for any tips. Maybe you have a completely different suggestion on how best to invest your money.

What do you generally think about our income, is this 3200 net enough to pay off a house worth about 250,000?

We are very grateful for any advice.