More about items:

Redemption and Athene's Unholy Grail are very needed items for a healer. Its only good to ignore them if you are strongly ahead in the match.

Ardent Censer is also a very needed support item. It can be easily procced with W from Summon Aery. But... If attack speed reliant characters aren't playing well, its best to focus on other items.

Mikael's Crubile and Shurelya's Revive are items you should build if someone on your team is extremely fed and can engage without much risk. Shurelya's Revive would help to chase down enemies even more, and Mikael's would help against strong enemy CC, which usually is the downfall of most hyper carries.

Boots aren't really essential as you will be on your allies most of your game.

Dark seal is usually great early if you know you can easily get assists or survive team fights. Mejai's soulsteeler is even better, so get it if you know you will never die.

Morellonomicon is usually best against strong healing characters like Sona, Soraka and etc.

Twin Shadows is usually a good aggressive option to locate and slow enemies. Hextech GLP-800 is a very good item to have if you are strongly ahead, but it shouldn't be prioritized over Twin Shadows.

Luden's Echo and Rabadon's Deathcap is just there for the greater AP, so ya might as well build em if ya want to do a ton more damage.