You can check the Land registry (ksiega wierczysta) online if you know the plot numbers.
Thanks for sharing actual knowledge.
The OP might find it easier to buy an old house which is about to fall down and then build a new one on the same plot. That way he'll avoid the need to arrange (and pay for) sewage, water, electricity and cable connections. Buying the land is but the first step in a long sequence of steps in which it is possible to lose frightening sums at every step.