Thank you for your input. I should have mentioned that I'm still fairly new to Gangplank, so I appreciate your constructive criticism. I'll look over my build again and make changes as I see fit.

*edit* Changes have been made!

I don't quite see the point of alternating your upgrades for Parrley and Remove Scurvy. Upgrading as a standard Q-W-Q-E for the first four levels and then getting your Parrley to rank 5 as soon as possible seems vital for Gangplank - he needs the damage and extra gold from his Q much more than he needs the heal from his W, at least if you're playing correctly.

Other than that, the only thing I don't like is the Quintessences - Quints of Desolation are better in the long run and more all-purpose, so you don't have to blow several thousand gold on Quints of Furor.

If you're not comfortable getting that because Last Whisper makes 40% of it redundant, replace the Last Whisper with a Youmuu's Ghostblade. Avarice Blade does wonders for Gangplank early on and the Youmuu's passive is amazing with GP's attack. The critical chance and the CDR doesn't exactly hurt either. In fact, if you get Youmuu's, you have enough of a critical chance to not have to get Seals of Malice - you can get Seals of Clarity instead, which helps Gangplank out with his mana problems.