they're not hard. soph's one is actually the back of a simplicity pattern copied then modified.
it's this shape and it's mostly guesswork since she grew out of the pattern I actually used to use lol!!
make the front first. between the red dots is 1/4 of the entire chest circumference.
the green dots are the height from shoulder to however long you want it to be (I do just beloow the knees cos my daughter's a running, jumping, climbing trees girlie)
for an adult one you may want to add darts but as I've never made anything for myself I'm not sure how to do that yet.
the blue dots are the natural waist, fron the straps down to there it should be fairy straight, but from there onwards it whould flare out a bit.
the pinkypurple dots indicate the strap width, I use a strap width of 2" with seam allowance 'cos it seems to suit soph.
the orange dots indicate an ease for the armholes. I normally wing this bit.
also, measure between the green dots and the line of the red dots cos that'll give you an idea of strap length at the front.
I've done a very basic picture below showing a single layer pinafore basic pattern idea (with facing). cut one of front, one of back and two of facing. if you choose to do a reversible one, leave out the facing and cut two of front and back.

oh how I love my tea, tea in the afternoon. I can't do without it, and I think I'll have another cup very
ve-he-he-he-heryyyyyyy soooooooooooon!!!!