Hi! From what I understand, you want to create an add-on or widget that users will use to create giveaways. The simplest way is to use an embedded iframe that gives the users buttons that allow them to share the giveaway on different social networks and sites(Facebook, Pinterest, Instagram, Tumblr, Tweeter etc). First they log in through the widget, then they can share and earn points or entries in the raffles/giveaways.
I've done a similar thing with a video sharing site, and it would involve a PHP script that delivers a HTML view to the end-user, along with a simple backend database to store all the user data(login, entries, points etc).
A more simple version would allow the user to share the event without logging in. After the user shares a giveaway, the shared entry(a Facebook like, a Tweet etc) would simply count towards his points or entries in the giveaway, and at the end the winner would receive an email in order to claim the prize.
I think it would take 5-10 days, it all depends on what sort of infrastructure you already have(server,databases, sites etc).
Regards,
Horia Porav