The right way to do this is to talk to the maintainer about how he wants the feature implemented first. Especially if it involves four weekends of work.
Depends on the size of the feature, and the maintainer, but you're right about "talk to the maintainter."
Some projects, you'll want to do a weekend of really rough work, contact the maintainer, get their thoughts. Others, you'll want to do 8 days work, get it far enough along to show, get their thoughts.
Often though, before you write a line of code, talk to them.
