I had the bathroom floor built up with marble tile about 1 inch above the current closet flange (PVC materials); consequently, I have to raise the flange. The flange attaches directly to a closet elbow so I don't believe that I can cut that elbow from the inside and extend it with a coupling, new pipe, and new flange.

I realize that there are extensions but then the closet bolts would be too short.

Any suggestions to raise the flange to about 1/4 inch above the finish floor?

If the flange is glued into PVC ell there is a way to cut the flange out of the ell and then install a short piece of PVC pipe and then a new flange that will glue on to the outside of the pipe.
Here is the way I do it. I use an electric saw and I cut away all of the old flange. I cut it down as close to the ell as I possibly can. Now with just a hack saw blade with some rags wrapped around it to protect your hands (they do make a handle that is for this purpose. I use the saw blade to make a cut straight up and down on the inside of the flange that is left, cut as close to the ell as you can get without cutting into the ell, when you have this done move the blade over about one quarter inch and make another cut another slot just like the first one, if you can turn your blade so that when you cut the little piece that is left will not look like a wedge but just a square piece. Now that you have made the cuts use a very small bladed screwdriver and put the tip between the two cuts and right on the line between the ell and what it left of the flange. Tap the screwdriver easily to make the flange pieces separate from the ell. Oh be sure and put something in the ell so that parts will not fall into the sewer. If it little piece comes out then use the screwdriver again where the ell and the flange meet, but you want it real close to where the little piece is gone that you cut out. Do not do any prying on the pieces just let the screwdriver separate the parts. Just keep moving the screwdriver around the ell and go very slow. If it does not come out easily you can always saw another grove in the flange and pop that part out.

G0good luck and let me know if this helped you.

How far do you have to go? I think they make extended wax rings for this. Tom recently posted you can buy up to 3'' closet bolts.

letmetellu, I was taught that method many years ago. It works if they used only clear glue. If it has blue glue or primer on it the hub will crack. Then they are in trouble.
before anything is done I think we need more info. Is the floor flange a 4" outside or a 4" x 3" inside or a 3" outside?
you can get a 3" inside flange in varying lengths and it will work but it restricts a bunch. you can also get 1/4" flange extenders and glue them down with blue glue [rain or shine glue] and use the 3" closet bolts that were suggested and use a washer and nut on top of the flange as well as on the toilet bowl.
long story short, I suggest spreading the risk. Hire a plumber to do it, pay him, let him carry the liability concerning a leak. You may save a hundred dollars on the plumber and spend a thousand on leak repairs below.