With the high cost of roof repairs and the key role a roof plays in protecting the home, you may be surprised to learn that home inspectors have no obligation to actually climb up and inspect the roof. Even the American Society of Home Inspectors, which serves as the industry leader in home inspections, does not specify how roof inspections should be performed. It requires only that members "observe" the roof, but leaves individual inspectors to determine the best method for each house [source: Solomon].
An unwillingness to climb up and inspect the roof doesn't mean your inspector isn't up for the job. It may be due to a lack of roof access, or slippery conditions. On very steep or hard to reach roofs, it's hard to fault inspectors for avoiding the climb.
To ensure the roof is thoroughly inspected, confirm with the inspector ahead of time how he'll check out the roof. You can also offer to supply a ladder and assist as much as possible with providing safe and effective access to different sections of the roof.