I buy fat quarters when I am planning a quilt that has a lot of variety in it. I have tons of fabric so that isn't the problem. I was making several jar quilts and wanted each jar to be different so the fat quarter were the way for me to go. I made a bunch with bugs, food, toys, etc. and that way I could get a lot of variety without buying more fabric.
I believe it depends on what project you are working on.

If you check at your local quilt shop, I think you might find that a 1/4 yd of material is about the size of a fat quarter and that it might be cheaper if you have to purchase material. I would use my stash for my colors instead of purchasing more material. It should be fairly easy to do.

Theoretically, a regular/long quarter of a yard should have exactly the same number of square inches of fabric as a fat quarter (assuming it's cut from the same fabric)

The difference is in the shape of the piece.

A regular quarter-yard is 9 inches long by width of fabric.

A fat quarter is 18 inches long by one-half the width of fabric.

A lot depends on the size of the individual pieces and if the print is directional or really large on which is the better buy for one's purpose.

Marcy J - can you please share the pattern name and a photo of the fabric you'd like to use? That will help alot in trying to determine if the layout is going to be affected by fewer fabric choices.

did you mention that you only have 4 fabrics that coordinate? and the pattern needs 16 DIFFERENT fabrics? IMHO is will be very hard to get the same pattern look with only 4 fabrics instead of 16. Test the pattern by making 1 block with the fabric and see how you like it. Or maybe you can just use the 4 fabrics in a different pattern. There is no need to cut you fabric into fat quarters- just cut the pieces according to the pattern from the yardage. If you really like this pattern then maybe you can just buy a few fat quarters to add to the mix. Or think outside the box by adding other fabrics from you stash that fit in but may not be "coordinated" .

The name of the pattern is Four by Four by J. Michelle Watts. I purchased the pattern on line. Thanks for your help.

It looks like the pattern has no one fabric touching the same fabric.

Will you list the link that you used to buy the pattern since you can not show a pic of the pattern itself. I am having a hard time finding this pattern on line. thanks!

Purchased from Annie's Quilts.com

I see your pattern. My opinion is that you need more than 4 different fabrics to make this successfully. The more the better.