A year or two back there was a proposal to relax the building law allowing permanently inhabitable buildings to be constructed but I think this proposal was shelved cos my friends would not have sold if the potential for development (and increased value) was still there.
The law was changed to allow foreigners to buy a " dzialka " about two years ago and many Poles bought up large lots in the hope of making money. I think you will find in this market which is very tight, if you have a buyer,especially a cash buyer you don't look a gift horse in the mouth.
As far as I am aware (My friends sold two plots last week) when you buy a działka there are restrictions on what you can erect on them (as Magda said)
1. you can build nothing.
2. you can build a summer house.
3. you can build a permanent house
4. commercial property.
2,3 and 4 require a permit,if you do not have a permit and want to change the status, you have to approach the man/women who has very greasy hands and likes brown envelopes.