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Its definitely an ambitious first project and would also of advised to start with an easier project....
Totally - just have to pick something ambitious enough that teaches you all the stuff you need for the big job - and it has to have a decent chance of failure. Without that you won't learn enough. What you pick would be a choice contextual to the person.
Failing to build a footstool will teach you a lot :)
Might teach you about buying rough sawn timber and the process of machining down using planer/thicknesser to the requisite size and making sure its square - may sound easy but there is a definite skill to it.
I do bits as a hobby and own all the machines required and would think twice about building garage doors ( I've already made internal doors ). Its definitely an ambitious first project and would also of advised to start with an easier project....