Hey guys, well, I dont know, if this is the right category to ask, but yeah 
I am working on a 2D Sidescroller and I want to have a system, that when you complete a designated quest, you can go back to your hometown and upgrade a house (like the blacksmith) I would appreciate an answer 
if you are also interested in helping me for a bit more stuff (mostly coding), send me an e-mail to brofiststudios@t-online.de
This question is so broad, that it’s nigh impossible to answer in a forum post.
I can give you a hint, though. Create the hometown as a scene. This scene functions as a hub to launch the individual sidescrolling stages, split into one or more scene. When the player finishes a stage, load the hometown scene.
Information on how to save global data (like the state of the hometown) can be found here:
http://unitygems.com/saving-data-1-remember-me/
Thanks mate ! I know, this is pretty hard to answer, but your idea sounds promising 