one approach i have used in the past is to drag the scrollview out of it's containing view in interface builder, and set it's actual size to what want the contentSize to be.
what is not inherently obvious about interface builder is you can have unassociated views that are stored in the nib, but aren't a part of the main view the nib is primarily for.
in the view where you want it the scrollview to live, place a simple UIView, which you use as a place holder. (this is simply so you can visually design it's location. if you are just using the entire view, you can skip this step and use the second code snippet i supply at the end of this answer).
you can then populate the scrollview with controls, visually laying it out how you want it to be. give both the placeholder and the scrollview properties inside your view controller so you an access them at runtime.
at runtime, in - (void)viewDidLoad
scrollView.contentSize = scrollView.frame.size;
scrollView.frame = placeholder.frame;
[placeholder.superview addSubView:scrollView];
[placeholder removeFromSuperview];
alternatively (if you didn't use a placeholder):
CGRect f = self.view.frame;
scrollView.contentSize = f.size;
f.origin.x = 0;
f.origin.y = 0;
scrollView.frame = f;
[self.view addSubView:scrollView];
finally, if you "lose" your scroll view in interface builder (it's possible to close it so it disappears from the design grid), don't panic. just click on it in the object list to the left of the design grid.