I would highly reccomend you exchange your Greater Mark of Scaling Ability Power for Greater Mark of Magic Penetration. The 1.8 ability power you gain over 18 levels is really not worth it. The magic penetration is not only better in game, but is also a more efficient use of your IP. You can let your personal preference steer you away from this, but during the early levels, when these marks only give .1 AP per level, the magic pen will help more.

It would also be nice you exchanged the blue, or bolded text in the guide with the icons. Now I don't mean every single items reference needs to be linked, but perhaps when you introduce the new item? This:

Mejai's Soulstealer
If you're going to get it, then go for it early game before getting a Rabadon's Deathcap so that the stacks build up.

Could turn into:
Mejai's Soulstealer
If you're going to get it, then go for it early game before getting a Rabadon's Deathcap so that the stacks build up.

You can link items (or your summoner spells for that matter) by putting two [['s on either side of the name.

Yep, my first guide. I checked your guide out, two defensive for my liking unfortunately. I like to play carry ):

I do prefer Ghost, comes in handy for chases indeed. Just lead a 19/2/1 carry and had to use Ghost to catch up to a few champs.

Exhaust is okay. I find that if I'm in range of them they generally don't get away alive and if I do get close enough like that, I usually have my ultimate off of cool down for that exact purpose - to slow them if I know my other abilities won't provide the burst needed. Though truthfully I'm thinking about subbing out Ignite for Teleport, just because I feel like it takes me ages to get around the map.

I do however think Ghost is bad choice but i can see it being nice to catch someone i prefer Flash. most times i go with Exhaust + Surge

Great guide! You put a lot of time n detail into this. Is this your first guide? I just made my first guide you should check it out n give me some pointers ;D its called Fizz on 'EM. Again great job

I've gone Mejai only twice in my match history and unfortunately, it wasn't the times I had a low death count. Fizz is great at getting out of sticky situations, making Mejai a viable choice. If you are concerned about purging your stacks then build another Rabadon's like I often do instead.

As for the rod of ages, you're right. It's just I rather prefer getting my AP built and having a Lich Bane, than worry about an item that won't provide as much.

To reiterate my item explanation; if you're having health/mana difficulties or being ganked, then build a rod of ages first after buying boots.

Fixed item build.
Removed the Mejai's to make for a safer choice.

Why would you get a Rod of Ages so late? A early game Catalyst would help with lane presence which can turn into a mid-game Rod of Ages to give it enough time to reach the max stacks to receive full benefits from it.

Also I'm not sure about the Mejai people generally don't purchase one anymore simply because snowball items are high risk items.