I build armor and Warhammer figures, so here are my two cents:
Hilariously easy: Sci-fi scratchbuilding. Fun, relaxing, completely unconstrained by rules and did I mention fun?
Easy: Reading Tamiya instructions. Building 40k stuff. Easy because the things have all the complexity of a brick (they need to be durable enough to withstand repeated handling, throwing dice at it and/or being dropped by Unsupervised Game Store Kid, my arch-nemesis).
Moderately hard: Cleaning mould lines and filling seams, working with photoetch components.
Hard: Painting figures. Gluing photoetch components (at least three times harder than bending the little sods)
Very hard: Painting vehicles (with a brush, mind you). Reading Dragon instructions
Inconceivably hard: Painting anything clean and/or with gloss finish, like cars.
Look at these people, these human beings; consider their potential! From the day they arrive on the planet, blinking, step into the sun, there is more to see than can ever be seen, more to do than... no, hold on. Sorry, that's The Lion King. But, the point still stands... leave them alone!
-- The Tenth Doctor