but I was thinking on creating a single square tile which has an one tile overlap to be able to create the scenario as it exists in real life.
That can be done. Although it is a very specific tile for a very specific use.
The best way to design the great hall of the station then could be:
-The segment in front of the tramtracks, without overlaps.
-The segment after the tramtracks
-Segments with overlaps. Not just the overlap for the slopes that I circeld, but also the overlaps further on in the station, the ones where the roof and second floor go over the tramtrack.
Keep in mind that public released grf's will be used by people all over the world that not all know the situation around the real life station. Having the overlaps fixed on the front-segment can create confusion for players that dont know how this station actually looks in real life. Having them as separate segments will hopefully limit that confusion as you then can place some extra information in the purchase-menu (under the name and picture of the tile), explaining the use of these tiles.
I hope that you are not too far yet in drawing those parts of the stations and that you can split it up in these segments.
Furthermore.... What would be very nice, is getting also the other 3 possible views. So, a front view that is simply flipped (and then has to be corrected for the right shading) and two backviews (also in this case, you need to draw one backview and then just flip it and correct for shading). That way the stations can be used in all 4 directions. This could be a lot of work (especially the backviews, as I dont think there are many pictures of those), but gives a lot more options and diversity.
I think your way of drawing makes this possible, especially when I look at the early drawing stage of the entrance to the great hall (it is also how I create new stuff). It looks like you start out with basic blocks that have the general shape and then add the features, textures and shading that makes them look like the real building. By using this early drawing stage it may be easier to also make backviews.
I look forward to your work!!
and about the licence under which I release these grf's, I haven't thought about it yet. but I'll release the station under whatever licence that is needed to allow you to use it in the additions set.
Here you can find descriptions of the most used licenses for GRFs: https://www.tt-forums.net/viewtopic.php?f=68&t=55814
My Dutch Stations Addition Set is licensed GPLv2, this is because I also used parts from the original Dutch Stations Set (that is also GPLv2).
But also in a nutshell, because I want it to be possible for others to use (parts of) my work without the need of contacting me personally. That way if my computer ever explodes, people can still use my work without waiting for me to reply
Finally, I already see in the central hall some elements from my set and the original Dutch Station Set (like the stairs, ticketboxes, trashcans and timetable information). Which is ok, because that is why those sets are released under GPL, but (as I understand it, I am not a copyright lawyer
) that also means that work that uses these elements has to be the same license. That could make your choice for a license a bit easier