When a character has spikey hair, you have three options:
1) An ugly wig (sorry)
2) A very spikey wig, that might not look 'possible' in real life, but has the right affect
3) A more realistic wig that is less spikey, but still does a good job of bringing the character life
In the case of Cloud from FF7, options 2 & 3 are the best! And both work really well, it just depends on what kind of wig you want to style!
This is option 2: the unrealistically spikey, but oh-so-accurate option! You can see this cosplayers AC Paradise account here.
I really love the final effect! Even though I don't believe this is real hair in anyways, I instantly know it's Cloud! To make this wig, he combined two Platinum Blonde Magnums before spiking this wig. For photo documentation with details on how this was achieved, check it all out here.
This is closer to the realistic look I was talking about! The spikes are still pretty intense so you get the feeling that YES this is Cloud, but it doesn't look like totally fake hair. It's a wig, but it doesn't look so styled that real hair would never achieve the shape, which I appreciate in a character as human as Cloud is.