Hi there!
Im working on my first sweater and the armpits have gotten me a bit confused. I’m not exactly working with a pattern, but rather several youtube videos for inspiration. I’ve had a bit of luck so far (its bottom up), but I’m getting close to having to worry about how many stitches to set aside for the armpits, and I cant quite figure it out.
Welcome to KH!
Making up the pattern as you go along is exciting and adventurous of you. Have you looked at Elizabeth Zimmerman’s percentage system? It’s demonstrated here:
http://www.knitty.com/ISSUEwinter04/FEATknitbynumbers.html
It deals with sts for the underarms as well as the rest of the sweater. I don’t think that’ll vary no matter which sleeve or yoke style you choose to work.
Cool! I make my sweaters up as I go along but I work top down to make fitting easier. What sleeves style are you planning to use?
This is EXACTLY what I needed! Thank you so much for your help (and for not making me feel bad about not using a pattern first) XD
Heres a picture of a puppy in a sweater to express my gratitude!
https://www.google.ca/search?q=puppies+in+sweaters&rlz=1C1AVNE_enCA682CA682&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjMgqDo9czSAhVN2GMKHej3Cd8Q_AUICCgB&biw=1366&bih=623#imgrc=GjQbMVwhbmMyRM:
Disclaimer: I made neither the sweater, nor the puppy!
I heard that direction was easier (and better because you can try the fit), but only after I was about halfway through! I’m using simple tube sleeves, in the most basic way possible. I made a sweater dress right before this (my first non rectangle), but it was sleeveless. Thanks for your help! 
Oh my, puppies! More than enough thanks. That puppy is adorable.
If you want to knit a pug - http://www.ravelry.com/patterns/search#view=captioned_thumbs&query=toy%20pug%20dog&sort=best&craft=knitting
