Hooded baby best?

I’m wanting to knit a hooded vest for my son, but can’t seem to find a pattern. Would anyone happen to know where I could find one or some this on how to alter a jacket? TIA

If it helps, he wears a size 3-6 months.

Welcome to KH. Ravelry has some; you might find one you like. http://www.ravelry.com/patterns/search#query=knit%20baby%20vest%20hoodie