Doors and Windows - Interior door framing

I am re-developing a basement and am having trouble matching existing framed and finished doors. So I will deconstruct them and reframe where necessary. Should my 82" RO height be from the subfloor or from finished floor?

Go with finished floor.

Hi your (RO) rough opening is just that! THIS IS BASIC FRAMING. From slab up! Trimmers are 81" for a 80" door "int. or ext" nailed on bottom plate then you will have a total high of 82 1/2. and your Header is placed on top of the trimmers and nailed to the king studs... If your door is 30"wide you will want your opening from trimmer to trimmer 2" wider, So your opening will be 32"! Your "header" for single trimmers will be, 3" longer, so 35" for HDR, If you use double trimmers cut your HDR. 6" longer 38" so the header will sit on top of the trimmers, "The jamb will fit between them perfictly" and from the slab to the header will be 82 1/2 "off of the slab" This will be for all doors that are 80"! all 6/8 doors start at 80" tall and cut at the bottom rail to fit your finnish floor!

ill do a basic layout for you, The "T's" are the trimmers X's are the studs and remember trimmers will be 81"

Single Trimmer layout int wall 2' & Go "NON Bearing wall"
x----x----x----x----XT--32"--TX----x----x----x----x----x

DBL Trimmer layout for int Bearing wall 16" & go or 16" oc
92 5/8 studs W/DBL top plate, for 8' tall wall W/green bottom plate if concrete subfloor! H2.5 or RSP4 with tico nails every other stud top and bottom.
strap hdr onto king studs and "Red Head the bottom plate to the floor in every other bay, little stud over the HDR called "CRIPPLE" to mantain your 16" oc and do not clip!

x----x----x----x----XXTT--32"--TTXX----x----x----x----x

THIS WILL WORK BEST FOR YOU if you get lost email me ill help you out
Steve