Okay if you want your character to be skin and bones that's fine with me.
But realistically his weight should be around 190, but hey EXTREMELY underweight characters are cool.
For a seven foot five full grown male, are you crazy? o-o
Did you even bother researching?
http://www.disabled-world.com/artman/publish/height_weight.shtml
http://www.halls.md/ideal-weight/body.htm
http://www.rush.edu/rumc/page-1108048103230.html
http://www.loseweightslow.com/weightandheightgraph.html
Especially if you say he's as muscular as he is he'd be on the even higher end of the charts.