Well, I wouldn't advise building in a cell that is modified by one of the very popular UL mods. Here is a nice map of them: http://i168.photobucket.com/albums/u187/K4tana/Untitled.jpg
(The bit circled in red is not a UL, it is the area that my WIP mod is modifying, but hopefully you won't want to build there either, since there are no roads there.

)
Also there is the http://www.gamesas.com/index.php?/topic/1064849-relz-new-roads-bridges-revised-thread-no3/ mod which you might want to build near.
Good luck with your modding