I am building my 1st park in sandboxmode, and it took me 1,5 hour to make the starting area before i had to got to do some irl stuff. It still isn't finished but this is what i did do for a good start. 
https://www.youtube.com/watch?v=1eO6CXqyGDw
https://www.youtube.com/watch?v=1eO6CXqyGDw