This is a morde build that I have had great success with and I thought I should share. I believe that having a morde with tons of damage and spell vamp is much better than one who is just a wall. This morde can get so much hp from spell vamp late game that you can go from 1 hp to full in 3 seconds.

Pros

Great dps
Great spell vamp works well with his shield
Can wipe out 3-4 people solo
Gives him enough hp back that he can tank baron or dragon easily

Cons
Really dependent on doing damage so if you get stunned and focused you are done
Squishy until you can get Hextech Gunblade

In my opinion Ignite and Flash are the best spells for morde as he can throw ignite with his ulti for an amazing dot and the flash is great for getting that last Mace of Spades on an enemy or just using it to juke an enemy team. Now if you want to use other summoner abilities the only ones that seem valid to me are Ghost to help offset his slow speed for ganks for fleeing and Exhaust to increase the chances of getting more hits off on an enemy.

Greater Mark of Magic Penetrationx9
Greater Glyph of Scaling Cooldown Reductionx9
Greater Seal of Vitalityx9
Greater Quintessence of Healthx3

Alright the Runes. You should definitely go for the magic pen runes as it will help out a lot early game with ganks. The reason for the hp over level seals is for the survivability as you don't have much hp otherwise. I go cooldowns for glyphs because as spell vamp morde you need your spells to be up asap.

For the masteries just go enough into damage tree to get the addition magic pen and after that go for the 9/21/9 for the survivability. Full dps isn't worth it to me because you need the extra defense from the tank tree in order to survive long enough to get your spells out. It is possible to go 21/0/9 as morde, you just need to make every hit count to get back as much hp as possible.

Alright with your skills you should be spamming your Siphon of Destruction as much as possible for the harass and so you get your shield up.

When you get close enough to the enemy use your Mace of Spades so that you get a good hit on them. If you are 1v1 this is your best friend as the bonus dmg is doubled if the target isn't near any other enemies.

You pop your Creeping Death if you are either being focused or your teammate needs it to survive a team-battle. This gives you armor and mr so it helps out greatly with your shield.

Now for Children of the Grave this skill is so amazing as spell vamp morde because it will damage them around 50% of their hp at end game with just that skill, also if you can pop your ignite they are easy pickings. The thing to keep in mind however is not to just instantly pop it on the first person you see, try to put it on either a strong physical dps or on a person with around 50% hp as it will greatly increase the likelihood of either getting a big dps ghost on your side or taking out someone with low hp so you can focus on the other enemies.

Alright you start out with Bootsso that you can get around quicker to hit people with your Mace of Spades. You get the three Health Potion's so that you can get enough hp regen to offset the cost of your abilities.

After that you head straight for the spell vamp with Hextech Revolver You should be fine with just building your Hextech Gunblade and Will of the Ancients before you finish boots.

After you finish those you get Sorcerer's Shoes for the magic pen.

Now you should be focusing on getting your rylais crystal scepter starting with giants belt for the increased survivability.

Now that you have some slows this should help your team-fights and ganks tremendously as you can hit their whole team with Siphon of Destruction to slow them all.

Now you have to see how much magic resistance they have on the enemy team. If they have a lot go Void Staff . If they either have a good amount of magic users or they have low magic resistance go with Abyssal Mask to lower their magic resist further while increasing your own.

After that, if you are still in the game you should go Rabadon's Deathcap for the ap.

If after loading up on elixirs you still have a lot of gold leftover its time to trade your Will of the Ancients for another Hextech Gunblade

Morde is a farming master, at low levels try to use your Siphon of Destruction only to last hit or harrass. As you level up your Siphon of Destruction and your Mace of Spades you can instantly take out mages giving yourself a lot of creep kills. If your don't have a jungler and wraiths are up on either side feel free to hit them with a Mace of Spades followed up with [siphon of destruction. This should allow you to kill the creep quickly, leaving you free to go gank mid.

Alright folks thanks for reading my guide. Just as a heads up this may take you a few games to get used to it, but it is definitely fun to play and wins a lot of games.