It was announced on Monday that the 51-year-old would exercise the option for a third year at the Demons following his initial two-year appointment in September 2013.
Roos has played a significant role in stabilising the club after a disastrous three years on and off the field when it won just 14 of 66 games.
He told Fox Footy's AFL 360 on Monday that he felt a sense of responsibility to oversee the club's rebuild and agreed to the extension after consulting his family over the weekend.
"We had a chat on the weekend as a family and the family were really supportive," Roos said.
"Probably the feeling was I was pleased with the progression we've made.
"Probably another two-and-a-half years rather than another 18 months, I think, will make a big difference. Then hopefully I'll hand over a really solid football club.
"You do feel an obligation. I can't go any longer than three years, I think I've explained that.
Melbourne has been competitive in all but three games this season, winning four but also losing five after being in front during the final quarter.
Roos played a key role in the recruiting of Dom Tyson from Greater Western Sydney, Bernie Vince from the Crows and Daniel Cross from the Western Bulldogs, which helped improve Melbourne's midfield.
Roos plans to appoint a senior assistant to work alongside him next season. Although no guarantees will be made, that person will be the prime candidate to become the senior coach in a succession plan Roos agreed to when he took the job.
All current AFL senior coaches are contracted until the end of 2014 but several come out of contract at the end of 2015 and 2016.
Melbourne faces the Brisbane Lions at Etihad Stadium on Saturday as it tries to break a record of 18 consecutive losses at the venue.
