Heya, thanks for the comment 
Yes, I still lurk around here and I’m going to finish that god damn last room in my map as soon as possible. I’m sorry for the lack of updates.
As for references, I really just make up things as I map. Usually I get inspired from other games I play, and then I try to incorporate some of the elements from there. Noteable examples are Team Fortress 2 and Half Life 2 episode 2.
However, this maps terrain is very crude, because I have to work within the confines that my friend left me in his original map.
. The bad news: due a lot of work I had not much time the last six months, have been sick at last for a month and so I added only a few details and decided to resize the map to the half size which means: the river part gets canceled and I’m concentrating completely on the old city part now which is already about 60% finished. I have still a lot of scenery brushwork around the finished central buildings to do and the river made not much sense anymore.
But thanks, I will try again, I think the exterior stuff is finished now. If you could upload the file, thanks! And if you need a texture, I’m converting my photos to seamless textures, so I can give 2048x2048 stuff