If you're new to programming I'd look at examples of how roads are done and connected on just a plain ol' grid. Otherwise if you want curves like in cities skylines, check this out:
Don't worry about "a network system for roads in a city builder and a system for buildings on it", instead go for one system of that at a time. First see if you can build roads in the way you want them. Then try to build the tools to let the user place and connect them. Then figure out how to compute grid cell sized empty plots on the sides of the roads for buildings.
