I was always under the assumption a barrel roll was a positive G maneuver. Aileron and elevator applied at the same time to complete the maneuver. Entry height and exit height should be the same. There should not be a 45 degree upline before the start of the maneuver or at the end. I double checked myself at the IAC website. This is what they have to say.

"The Barrel roll is a combination between a loop and a roll. You complete one loop while completing one roll at the same time. The flight path during a barrel roll has the shape of a horizontal cork screw. Imagine a big barrel, with the airplanes wheels rolling along the inside of the barrel in a cork screw path. During a barrel roll, the pilot always experiences positive Gs. The maximum is about 2.5 to 3 G. The minimum about 0.5 G." https://www.iac.org/legacy/aerobatic-figures#BarrelRolls
This photo has always been my conception of a barrel roll.

I found this explanation here. file:///home/chronos/u-602a21254c188237162d19257f2dfec286b0e8fe/Downloads/SC4_Vol_F3_Aerobatics_14_Rev_1%20(1).pdf

F-17.07 Barrel-Roll From upright, pull through a 1/8 loop into a 45° upline, perform a barrel-roll with 45° spiral pitch, perform a45° upline, push through a 1/8 loop, exit upright.

I "think" they are trying to explain a classic barrel roll with technical term. Somehow it just doesn't translate.

With the above said I am not an accomplished aerobatic pilot. I do, do a pretty good job of faking it though

Ken