Why Rylai's should not be built on Singed.

There are many times I see Singed's and 9/10 times, after Rod of Ages, they're grabbing Rylai's and I just shake my head. You might as well be grabbing Hurricane for Draven. When I point this out, everybody questions "dude, it's HP and AP. I needs" but nobody really equates Singed's passive. I'd finally like to point out something people (pros) are finally realizing. Seraph's embrace on him is awesome. I've been using this since I first heard it procs off ANY mana expenditure and it's been awesome. Let's stat crunch real quick:

Rylai's Crystal Scepter: 80 AP 500 Hp 2900 gp

Seraph's Embrace 60 AP 1000 mana 10 mp/5 2700 gp

If we remember Singed's passive, that means Seraph gives 250 hp. So, not only does Rylai's have more AP, it has more HP. The only benefit is Seraph's is 200 gp less (so like two wards and some pots). So why? Well, let's remember Seraph's passive.

Insight: Gain ability power equal to 3% of your maximum mana.

If you've been stacking Mana for Singed's passive, you will now be doing awesome dmg. Assuming you're only equipped with a ROA and a Seraph's at lvl 18 this will net a total of 2475 leading to 74 AP extra leading now to Seraph’s providing 134 AP. Boom. So more damage. And chances are, you’ll grab Frozen Heart as well giving an extra 12. Now, about HP? Rylai’s gives hp and Seraph’s gives half as much only because of Singed’s passive. Well, what about Seraph’s active?

Unique Active - Mana Shield: Drains 20% of your current mana to shield yourself for an equal amount plus 150 for 3 seconds (120 second cooldown).

Once again, that’s 2475 mana giving you an extra 400 Hp shield which is only going to grow when you grab that frozen heart. However, this assuming your initiating with your shield. Rylai’s passive? You slow enemies for 15% movement speed, something that a well placed Super Adhesive should be doing better at anyway.

Not only that, but because Tear of the Goddess can be charged in lane, it's why it's one of the first things I rush. You can charge it while recalling, while in base buying, seriously, just leave the thing on and you'll have it charged in around 5 or so minutes. That's about 200 hp. If you happen to be unlucky and get a nasty lane match up, you're still able to charge your Tear.

TL;DR Seraph’s Embrace provides substantially more AP than Rylai’s and while, only providing half as much HP, it’s shield more then enough makes up for that. Building more tanky mana items to help Singed’s passive also makes you deal more dmg. Also, mana regen and passive hp in case of a nasty lane match up.

TL;RDR Seraph's > Ryali's.

EDIT: Forgot to factor in ROA being fully charged. Oh well :)