1st thing what a funny idea to want to model a rock under SW, it's not made for that!! If you're new to SW, starting with a boat hull, even partial, would be simpler.
For your problem, your sketches would already have to touch each other, this is not the case at all.
You should start with mechanical parts because if you manage to do them for the baccalaureate and especially for the rest of your studies it will always be useful to you (unless you are a pro at philosophy).
A funny thing to do, for example, to get your hands dirty
Yes but you can do almost everything with SW and as I am in the project of modalizing a lighthouse I would like to make the rock on it. And how do you do that with "half sketches"?
Or have fun making it on blender for example (free) which will be more suitable for fancy shapes. Or even find ready-made ones, but less glory, but not necessarily a bad thing since what in a mechanical or other design you have to use commercial parts instead of studying and making them in your own way, is a saving of time and money.
Uh... No... a cube for example or a cylinder with a rock texture, a base ^^.
But now I'm afraid you're trying to ride a racing bike before you've learned to fit on a bike, it's pictorial of course but that's the feeling it gives me.
Simple to start with, don't torture your mind trying to make a rock with all the deformations of time, wind and oceans.
The most important thing in your design is the lighthouse and not the rock ;)
as they often say, you can't go faster than the music^^
Model your rock with triangular facets so that it locates the place where your lighthouse is placed, which is the real object.
And then facetized shapes are fashionable, it will look a bit geeky.
Kind regards
PS: several of my very knowledgeable and experienced colleagues make relevant suggestions, but if you don't want to follow our recommendations : then I don't think it's much use to continue the discussion that goes with what you imagine you can do.
Groucho Marx (not to be confused with Carl): I tried to play the piano several times but I think it's impossible to play this instrument.