I was wanting to know of any good ways to mount speakers in the roof. Its an f100..

 

There's really no good way to mount speakers on the roof. It would depend on size of speakers. You can get creative and build a holder for them, utilizing the cross bar in the center of roof. Or you can go completely custom and have them installed when you do an interior upgrade. Choice is yours.
I do knoe there is a headliner for sale that has an area for speakers and a radio. Search this forum for the headliner.

 

Get a highliner... it provides four speaker locations and also has a place to put the deck. I've seen 'em used for $100 on CL.

Here's an installation guide: 1972 Ford F100 Stereo Speaker Highliner Headliner Installation - Classic Truck Guide

.. available from LMC: Truck Parts and Truck Accessories

 

this is how i did mine 4 years ago when i was in high school