The grammar and spelling errors make my eyes hurt tremendously. I know you said in the comments that you're not used to using BB code, so I'm not gonna dock you for that.
I also think sheen may not be the best item for Morde. I know that it can be helpful, not sure about the 1k damage you mention in the build, but I just think there are other alternative items that can be more of an overall benefit to you than an item that gives mana you don't need and only really supports one skill.

Would love to give you a +1, you're on the right track. Not saying you need to change your build or your guide, for that matter. Your build is your build, and I'm not one to downvote because I don't like the way you play even if you're successful with it. Copy/paste everything into microsoft word to do a quick grammar/spelling check and I'll most definitely change my vote :D

alternative items
skill sequence , team work , farming, lane and counters ...

Your guide need more details it's very poor but i dont like that warmog change for a rilay (Y) i dont wanna -1 you cause its :s stange criticals comments :cc

Your guide needs more detail when talking about abilities and when i should/shouldnt use his ulti and against who.
This guide has all the info is messed up and has walls of text, when i tried to read it i got lost and had to start again several times.

"The target's magic resist is treated as being reduced by an amount for purposes of damage calculation, but cannot be reduced below 0. Flat magic penetration stacks additively."
go learn to play noob

9/0/21 is a bad choice so is warmogs and zhonya.

buying mr before hextech isn't effective and buying rabadons as last item is just stupid

On a side note try not criticize other people guides before you do research

very nice guide for newbies

Thanks for the advice,
I turned on Require comment to vote.
i'm still new on mobafire, don't feel very confortable with BB code to put icons, split my space vertically and other stuff ...
if you have any advices to make my guide look better, i'll be thankful.
(just voted up for your zyra guide :p)

In order for your guide to succeed, you'll have to put it through a grammar cleanup and turn on Require Comment to Vote. Professionalism is essential for any guide to succeed.

Good luck! +1