This is a Morde build I randomly came up with while fooling around in normals one day.
This build is mostly AP/Tanky but taking more of a survivability route.
With more spell vamp and more MR + Armor you can initiate better as well as survive longer.

With marks you get the early magic pen to harass and poke a lot better so magic pen is a must.
The seals and glyphs I use AP per lvl due to getting solo XP 99.9% of the time since you will have a solo lane. This also helps to get your E to hit harder
Quints I use flat AP so early game you can dish out some dmg in your lane.

I use the 9/21/0 build due to more AP + the 15% magic pen is nice.
I also go 21 in defense due to the 5% less dmg done to you and to have better survivability in a 2v1 lane (if the other team doesn't have a jungle, which is rare to see)

I still start Regrowth Pendent because of the early health cost of his abilities.
You can sit and regen most of the health lost from spamming his E.
When I back I usually have enough to finish a sorc boot or a boots of speed and one amp tome.
After farming more finish off the sorc boots if you didn't and start building the rylai's.
Always farm enough to finish rylai's and get a revolver if you can.
After more CS get Gunblade, Gunblade's active plus a good Q,E combo along with ult will pretty much insure death, finished and start either build FoN (Force of Nature) or Randuin's depending on the other team comp and to have more survivability.
You want to finish off with the WotA (Will of the Ancients) for a total of 50% spell vamp and 25% spell vamp for your team along with 30 AP.

At the start you always want one point in Q,W,E for the harass and for the survivability with the armor and MR increase from W.
After that E takes priority but always keep Q,E one point higher than W.
When going the AP/Tank build I suggested, poking is your key dmg to make them back so you will have the exp advantage.

Ghost: Always carry ghost its good for escape and gap closing.
Ignite: Is a MUST! if timed correctly with ult you will get the ghost 99.9% of the time unless they have a kayle who times invuln correctly or a quick silver sash or a superb support.
Flash: Decent summoner spell to take but the short distance port isn't worth it much since you have a rylai's.
Exhaust: Good on basically any champ but more MS is better.

HUE HUE HUE.
With this build and smart people to help focus down focus targets you will lead your team to victory :D.
Also make sure that the team does not i repeat DOES NOT attack the tank.

Most ranked games people know to not initiate on the Morde due to his shield.
But due to the recent "nerf" on his Q's dmg, along with shield gen on creeps he is much easier to take down.

Pro:
Good dmg
Good survivability
Nice MS
Great farmer
Can make a team fight into a 6v4
HUEHUEHUE

Cons:
Can't initiate that well
No CC at all
Requires a solo lane to do well
People hate him

NO JUNGLE ALWAYS SOLO LANE MAXIMIZE CREEP FARM.

Smart players will make any game easier.
They should help focus down the Ult target to ensure the ghost.

His shield grants him the ability to survive in lane better.
His E has a tad longer range than the indicator shows.
Q can bounce from creeps to champs on the tower and not give Morde aggro from towers.

One of the best farmers in game.
Even if shut down, with his farming abilities it doesn't matter much.