What you are experiencing is normal. How much elevation you loose on an aileron roll will vary with the design of the airplane, plane speed and the roll rate but all planes will tend to fall some when you roll. Don't change the elevator rate to address this. You have to fly it. Get in the habit of bumping elev up (pull elev) slightly just before you start the roll and then when the airplane is inverted bump down (push elev). As you move to higher performance planes, you will need less of this.