Placing an ad on the back cover of the Construction Specifier magazine costs $6,645. We have gotten several of our clients' projects on the front cover largely because when the editor called us we had the photo available. That's at least a $7,000 value, probably more because it gets online space as well; good return on the few hundred dollars our client spent to get the high-quality photo.
Magazines generally need a cover photo in a "vertical" or "portrait" orientation, or at least one that can be cropped to fit a cover. Pay attention to how the publication designs its cover; you don't want the magazines name, for example, to block the view of critical details.
Each magazine has its own look. For example, Construction Specifier runs images of completed buildings. If your product is a structural material buried beneath the surface of a wall, readers may not actually see your product. Still, there is value to providing a cover photo. For example, the use of your photo on the cover almost assures that your article will be named on the cover page, attracting greater interest to your article. It also enhances the proprietary value of the article or reprints by showcasing a project on which you worked.