Good morning
@bamminjammin and
Welcome to Radio Reference!
The wattage specification of an antenna is the maximum amount of transmitted power that the antenna can withstand before the antenna suffers damage. You asked:
Can a magnet mount hold a 102 inch whip as far as power?
Mag-mount antennas can handle whatever maximum power rating is specified. For magnets to hold a 102 inch whip going down the road at 65 miles per hour, a special heavy duty four-magnet mount is required. Here is an example of such a mount:
Check out this Walcott Radio 4MAGTM at www.WalcottRadio.com
www.walcottradio.com
Now you say that you are planning to place this on the metal roof of your house. Why not instead go with an actual base station CB antenna? Something like the following might be more appropriate:
Check out this Walcott Radio PT99PCGPK-1 at www.WalcottRadio.com
www.walcottradio.com
That antenna, of course, would be mounted on a pole or pipe fastened to the roof or the side of the house.
Finally, these items are just examples to get a discussion going. They are not necessarily the best solution or best products for you. Let's talk about your application in a little more detail so we can all help you to get the right antenna system to meet what you are trying to achieve.
Cheers! Dave