This is Poland so get everything in writing.
Good advice. Get any contract translated if you do not speak/understand, Polish.
Beware of clauses, such as:-
Full payment will be made even if we do not finish.
We have the right to use second hand materials if they are cheaper.
We reserve the right to decide what is an acceptable standard of workmanship.
Deadlines and timescales will be adjudicated by the standard reference. (Grimms fairy tales)
Any disputes will be settled by the building inspector who is a friend of ours.
European edicts on unfair contracts/consumer law will be superceded by Polish Law.