A T-28 shouldn't have any trouble rolling well. Set your ailerons to give you a full roll in maybe 2 seconds. That's fast enough that even if you totally botch the maneuver you'll still be upright in time to save the plane. Start learning by giving the plane a bump of down elevator while it's inverted. If you can visualize clock number positions give it maybe half down elevator from 8 - 10 o clock. You'll have to play with how much it takes, but you should be able to go all the way around without losing any altitude or changing your heading left or right. Once you can do that, back the aileron throw to give you roughly a 3 second roll, then work on feeding in that down elevator smoothly so that you're at maybe 15% down at 8:00, 40% at 9:00, then 15% again at 10:00. The actual amounts will vary from plane to plane, but hopefully you get the idea. Many planes benefit from feeding in a touch of down elevator early to offset the tendency to pull to the canopy in knife edge so maybe it's 10% at 7:00 or thereabouts for your particular plane. Once you have that figured out, the next step is to do slower rolls and use the rudder at 6:00 and 12:00. When you do that, you'll find that you need a lot less down elevator at 9:00 and everything will be much smoother. At that point, you can fly your rolls as slowly as you want to, even adding in 4 point rolls as you figure out the setup that make them work the best.