all havanese puppies are weaned in puppy pens with doors to the outside, their mother is kept in a welping area with a doggie door too and they see her go outside, when they can craw out of the welping box they follow their mother outside, so the transition to go potty outside is easy, doggy doors are about 60 dollars. some are more and some are less. if you are in within 100 miles of my home one of my door installers can do yours too, i also recomend a small enclosure on the outside (not the whole yard) of which they can do for you too if you like, 
every puppy potty trains differently, i send you home with a book on how to potty train. my puppies have the freedom to go out and potty without holding it or asking to go out. so they dont get used to going in a crate, or area inside.  a doggy door is the way to go. but if you decide to let the dog in and out he will atleast be used to a clean crate and potty outside.