In short - "A LOT"
But don't let that stop you.  Hobbies last years if they are a good hobby, so plan to take a few years to do this aircraft.  There is a ton of help here ready from the people in this forum.  They almost alway come up with an answer to a question with in a day or two.
To get started, copy the info documents off the Flight Sim CD's onto your hard drive and also load GMax (it is free on the CD).  Open the tutorial for GMax and start on page one.  Each item in the tutorial can be followed to make an aircraft part instead- for example - use the array tutorial where they have you make a spiral stair case, and make a turbine section of an engine instead.  etc, etc.
You can borrow an AIR and CFG file from an other aircaft initially (untill you make yours) to see your aircraft in the game.
That is for starters.

Harold