Grasp is better if you want a defensive playstyle.
Warlord's is better if you want an offensive playstyle.
I'll upload a screenshot of my trees when I get home.
EDIT: Warlord's page here: http://puu.sh/qrRSy/dd0a7304d4.jpg
Grasp page here: http://puu.sh/qrRUS/0f8db72a86.jpg
Your runes are fine, but scaling MR is better for glyphs imo and MAYBE scaling health instead, for seals. I also like flat armor pen for marks because she has some of the highest base ADs in the game.
Your core build needs a lot of work.
Illaoi is an amazing splitpusher, but she's okay in teamfights as well.
Core items:
Death's Dance for SP build/Black Cleaver for TF build
Iceborn Gauntlet in general
Spirit Visage
The MR boots with the CC reduction
Situational:
Sterak's against hard carries
Maw against specifically AP carries
QSS/Mercurial against a lot of CC
So on and so forth.
Building her as a tank is suboptimal because she needs AD for actual damage and is useless without it. She's not a tank, she's a lifesteal bruiser/juggernaut.
I always max W last. Just not rewarding.
I max Q generally.
E against a super easy bully lane usually.