May I suggest some things?
Please take note that this is all suggest and I love your design, so taking my input to your use or not is totally up to you.
I love the Elderwood line and honestly I feel like Elderwood Warwick (Elderwarwick?) would be a great addition, but I want to help you with your design because right now this looks closer to an Earth-Rune skin like Skarner or Xerath, and not Elderwood.
Lets take a look into the current Elderwood skins, shall we?
http://i.imgur.com/ZCmCISs.jpg
So, Elderwood Bard. We have a lot of blue theme here, and looking at the lighting he's part of a deep and dark part of the forest. But with luck, there is still light, with the local fungi and Bard's lovely meeps illuminating the place. Look at Bard's flow of design, and how the Elderwood theme isn't forced, but actually incorporated into the skin. Bard's arms, face and body in general is made of the wood of a tree, naturally rooted and not choppy or artificial-- a natural design. And the red maple leaves add a complementing color to the blue, as well as going into coordination with the wood, as if the leaves are sprouting and growing off of his tree-like body.
https://static.lolwallpapers.net/2016/03/56dab37159af9.jpg
Now we have Elderwood LeBlanc, which takes on a red-orange and aqua marine feel. Her body and her surrounding makes up for the aqua marine, creating a calm environment and inspiring a hidden-like grove to LeBlanc's background. And especially if you look into her initial design, she kind of takes on the theme of a river spirit, sprite or fairy almost, enacting as it's hidden guardian (Again with the hidden theme, which also greatly complement's LeBlanc's role as the deciever, with all her stealthy sneaky stuffs) And again with complementary colours, an red-orange accompanies her design in her hair and flower-staff, creating a mixture of color and theme that makes her seem mystical, yet deadly.
http://na.leagueoflegends.com/sites/default/files/upload/hecarim_elderwood_1920.jpg?itok=pPnl-zZp
Possibly my favourite, Elderwood Hecarim follows a bright, vibrant green theme, and displays the guardian of the forest theme just like Bard and LeBlanc, but more fiercely. He looks like the kind of spiritual guardian that come hack you down after you decided to go logging in his forest. It looks like your average forest, with deer and birds amok, but once trouble stirs Hecarim will show no mercy. Hecarim especially expresses an ancient tone to his existence, with withered and old stones added to his lower body, and a little bit on his left arm. He follows Bard a lot in this design with the wooden bodily features, and especially the leaves sprouting from his body really do compliment that trend.
Overall, they are the guardians of the forest, with natural flows, and a specific part of the forest.
Now, to incorporate Warwick into this, lets take some inspiration from the current Elderwood skins.
Hecarim is a bright green, LeBlanc is aqua marine, and Bard is a deep blue. And to allow Warwick to meld in with that, we should definitely have a base colour theme.
What color already affliates with Warwick heavily? If you said red, you'd be very correct.
I think Warwick could take on an autumn theme, with orange and red assorted leaves. His body could be made of roots and wood, naturally flowing around his body. I feel like he shouldn't have any stones on his body like Hecarim, since Hecarim is big and he can take it, but Warwick needs his speed. So I feel that his face could be either the autumn leaves or even continue with the wood body onto the face, but overall he should definitely have glowing red eyes. And over his wooden body, to continue Warwick's blood hunter savagery while still keeping the guardian of the forest theme present, large claw marks should decorate his wood body, as if a werewolf is marking his territory in the woods.
These are my suggestions, as well as my two cents. Either way, you've got a lovely skin concept, and I'd definitely love to see more work from you, as well as this skin being implemented some day (Maybe even with the Warwick rework coming soon too!)
