If it's a two-part wing, getting the wing joint / dihedral correct and fitting well together.


Covering? Nope.. that's just tedious and takes a lot of patience.
Sanding? Nope.. you get out of it, only as much as you put in.
Control rods? I can see that.. especially if it's a smaller plane and space it tight.
Motor mounting? I can see where that's a hastle.

My biggest problem with kit building is sometimes you have do keep several factors in your head at the same time. "If I do 'this', it impacts 'that' and I have to adjust 'this other thing' to compensate." Sometimes there just isn't a clear path or list of things to do..