Licence of the project is GPLv2. This means that when you modify this set or build upon it or its parts, you have to provide the source files of your work. If you incorporate something from this into your project then now your project has to follow GPLv2 licence too. This means that this licence is viral, so please, handle with respect.

This also means that this set can only include works that are compatible with the GPLv2 licence. In general, the work should be licensed as GPLv2 work or work should be in public domain. This means that if you are author and your feel that your work belongs here then you have to licence your work accordingly.
This also means that separate authors permission is not required if the permission is granted by GPLv2 licence or when the work is in the public domain.
This also means that if you feel that something from this set would be great in the one you are creating (or you think that author of that set should also include it in its set) then you are free to use it without special permission given your project licence is compatible with GPLv2 (unless you are reusing work that has been in public domain previously, derivatives of the public domain do not have to follow GPLv2 licence terms).
This especially means that when you do not like certain aspects of the set then you are free and encouraged to modify its source to have the version that pleases you.

One of the functional requirements of the set is that the buildings must have consistent floor heights. This is so far only hard requirement.

This is first post of the thread and will contain latest version of set. Including the source of the set. Please refer to the individual posts to see the intermediate versions.
Current version is 0.1.1. This is still a very alpha release.
This work is based on the previous work of tadeusz and Quast65 who were generous and smart enough to licence their work under GPLv2.

Polish Building Set by tadeusz was so far to my knowledge only openly available building set based on NML and Quast65 wonderful templates made the slicing up the graphics work of the past.