Finished?? I don't anyone on this board is ever finish, because once you do assemble a complete Fett then you get in this vicious cycle of upgrades.
Seriously this is not a black or white type of question, how long it takes is a big variable, some folks have been working on their Fett for 2 years or more while others have jumped right on in and manage to piece one together in a few months. If you have a lot of money some where around $2500 you can buy everything ready made sometimes even completely painted. If your like me where money is a big issue (that being there isn't any) then that means constructing everything yourself, so then it is only a matter of how much time you can dedicate each day to the project.
Since we just adopted a 3 1/2 year old little boy, for me I don't have a a lot of time, maybe 45 minutes to an hour in the evening 3 or 4 days a week, if I'm lucky. So far most of my time has been devoted to doing a lot of research and designing templates and drawing blueprints. So to be honest while have collected probably 75% of the materials and parts need for a Fett I still have a lot of construction and finishing to do and I have been at it for nearly two years, though it certainly doesn't seem that long. Nearly all the templates and blueprints are nearly complete, still working on the gauntlets so I am expecting things to start coming together pretty quickly from this point on. My goal is to have it ready by April for Norwest Con here in Seattle.
Hopefully I haven't scared you off, all of the templates are posted here on the Dent and are available to everyone so that should save you a lot of time in building the pieces and there are some fantastic painting and finishing tutorials. The Search function is your friend, plus this is a great community of very helpful people so if you ever get stuck there is always someone here willing to answer any questions and help you get through the sticky bits.