I haven't done adult sweaters top down, only baby ones. The problem I had is that they're all so different. I didn't like the Knitting Fool pattern generator. The sweater ended up being much too wide and large for what I wanted. I found a good baby sweater pattern and adapted it. That one was for a vee neck. I discovered that to make it into a button from the sweater neck front, all I had to do was increase the stitches in the front. The front and back stitches between the markers are going to have the same amount of stitches. A button band will then be knitted along the front opening edges. I figured out the proper sweater dimensions by looking at ones at Lion Brand's pattern website. They had a cute crochet sweater that was for beginners. It was all rectangle pieces that were sewn together. They had the dimensions of the sweater pieces all marked out for me. I figured out that for a newborn sweater, I needed it to be 10 inches across (a total circumference of 20, 10 front and 10 back). I kept knitting that top down sweater and measuring across the back from raglan seam to seam along the bottom edge of the knitting. When it got to be the right width I wanted, I stopped increasing and divided it for the sleeves. Your measurements may not line up with the pattern. You may have to knit a few more rows to get where you want. This is how I custom fit a bad pattern by measuring across the back. I knit the sweater until I reached the sweater length mapped out for me by Lion. I also used Lion's measurements for the sleeve length. This was a standard newborn pattern, as I didn't have the baby here to measure.
What you have to remember is that there are certain factors which make a big difference in the sizing. Who did the designer make the pattern for? It makes a big difference if she made the baby sweater, for instance, for a standard 7 pound baby or for the designer's big moose 10 pound baby. Does the designer knit tightly or loosely? That affects the pattern and size. The gauge listed, if there's one at all (many times there's not in blog patterns), is for the designer's gauge, not yours. That's why it's important to swatch to see how many stitches per inch you get. Another thing if you're a beginner is that the yarn has everything to do with it. If you use sport weight yarn for a pattern which calls for worsted, you will use more yarn, more stitches, and your sweater will be too small. Knit a swatch and measure before you start.