First of all, make sure it's indeed Bitcoin, since Altcoin giveaways are completely disallowed.
I've found this (see quote), which looks rather scary, still similar things are tolerated in [url-https://bitcointalk.org/index.php?topic=5310543]collectibles raffles[/url].
So, I think that, as said in the quote, Games and Rounds is the choice you have, or link to external site.
Most giveaway threads are no longer allowed in the Alternate cryptocurrencies sections. From now on, posting or replying to such threads could result in being banned. Existing threads will be locked.
Specifically, you are not allowed to give people any incentive to post insubstantial posts in your threads. You can't offer to pay people who post their addresses, usernames, etc. You can do giveaways off-site and link to the giveaway page in a thread, but you can't give people any bonus for replying to your thread.
Similar threads are already restricted to Games and Rounds in the non-altcoin sections, but the giveaway-related post volume is so high in the altcoin sections that I've decided to just ban them entirely here.