I wear a size medium shirt in most instances, bust is 34HH.  I bought a medium and it fits great.
The material is nice quality.  The cut is very flattering for a larger bust.  However, if you're on the taller side this isn't exactly what I consider a maxidress.  I'm 5'0" (not a smidge taller) and this comes right to the ground but doesn't drag on it.  It wouldn't hit the ground if I was any taller.  Now, being a short female this was a VERY pleasant surprise to me.  The chevron pattern isn't very noticeable, it does appear more horizontal, but that doesn't really bother me.