Building your own door frame
Speaking for myself (and certainly not for anyone else that that answers questions), I think the BEST way to learn is to either take a look at the 'wood parts' of other door frames on walls that are the SAME thickness (in the house), or to take your measurements and visit the Home Center and measure up there. W/O being able to see what you have, I'm not sure I can help you w/o managing to leave something out.
Between the 2 of you, you have to know someone who knows someone that will do the work for a pizza and a case of beer (or 2.) This would still be a LOT cheaper than hiring a Pro outright.
My best to ya and hope this helps.
Jay J -Moderator