Need Help With Interior Doors

I have a 91" x 91" area of entry into a room I'd like to make into an office. What are some inexpensive ways I can install some type of French Doors or other door system to fit this area? Would I have to add more drywall? Any idea of cost for this type of project?

 

Tommy2x, welcome to the forums. Aside from having custom work done, yes, you would have to frame in the sides and top to a more standard size. Nominal door rough openings are 82", and the width will be 2" wider than the size door panels you order. So if you get a 72" set of doors, the rough opening would be 74". This will give you enough shim space to make sure the door is square and plumb.
If you decide to do this, you will have to remove any molding and casing that exists. If non exists, you will have to remove the metal corner trim on the edges in order for the new sheetrock to lay flat and have a good seam on the repair. Post back if we can help further.