Custom Buildings

[WasakBasak]

Hello Hello
I recently looked into the Editor and used it to create a custom building. I used the German High school and decreased the lot size to 8x2 which I was very happy with, but it seems to have caused some error and broke the game (resolve error on Asset "German Highschool Small")
(I did a clean reinstall and the game runs as normal, but that building is gone.)
Could someone explain how the asset editor works and if I can create custom buildings using mod pack assets?
Many thanks!