Well... that is really, really up to you. But here's my opinion:
Druddigon's defense ain't purdy (if you know what I mean. Base 90 defense is not something to laugh about.), and some quick Dragon Dances and Dragon Claws from a Haxorus could kill it to the bone.
In other words, he really dosen't fit as a wall. Walls are Pokemon with some heck of a defense stat, and Druddigon certainly doesn't fit there.
And as a sweeper?
Well... 120 attack is quite impressive, and that's the stat that makes Druddigon shine the most. A couple of D-Dances could spice this thing up and make it deadly as heck.
There are more dragons wayyyyyyy better than poor ol' Druddigon. His speed is what REALLY kills him to make him shrudder, and that competively, he really, really, REALLY sucks (to me).
But that's your choice! Make him what you want!