Fix your mic.
Also, you seem to enjoy using her ult without using the Q, which I find odd. That Ezreal would have been a dead boy had you used Q on Sejuani instead.
As the one comment on the video said - the lane compositions cause me to seriously question the viability of your guide. You are clearly not playing a ranked match.
I'm a personal fan of grabbing Catalyst - Rod of Ages on Diana, as she is in the middle of fights and needs the extra sustain, plus she has mana issues early, and the Catalyst actually provides awesome sustain with its passive while leveling in the jungle. You could grab HoG and Phil Stone for these but they don't really build into anything useful for Diana, so I prefer not to go the gp5 route with her. DFG I could see as viable on her though, so maybe a Kage's Lucky Pick, but that would be the only one I would consider.
Also I feel like, especially since Abyssal Scepter got nerfed, it's a very good item on Diana in place of Void Staff. Leave Void staff for your AP Mid. You are in the middle of fights so you BOTH benefit from the passive of Abyssal Scepter, and it just provides a ton of utility for your team that basically only you could provide (with the shortened range of the passive).
Also, attack speed on Diana isn't nearly as good as people think it is. I tried it for awhile but got better results by sticking to tanky AP items like Abyssal Scepter and Zhonya's. If you try to build Diana like a mage you are going to fail, she's an AP Bruiser and needs to be built like one. It's the same argument as someone like Gangplank or Xin building pure damage - they can pull it off from time-to-time, but they provide the team with a lot more utility by building Atmog's/TF and some tanky DPS items.
The strongest utility that attack speed provides Diana is pushing power - pushing dem turrets to oblivion. In a teamfight it's mostly wasted unless the team is stupid and isn't focusing you.
By the way I'm like 65% win rate with Diana in ranked, 50+ games played with her, if that means anything.