This is my first experiment in creating my own non-dishcloth/scarf pattern. It uses Bernat Cottontots. It looks and feels a little heavy for a tank top, but in my part of the US, where during the spring and fall it can go from 40 in the morning to 80 that afternoon, this is exactly the kind of transitional top that is perfect! Plus, worn over a T-Shirt would be adorable. I eyeballed it based on some of my daughters 2T tops, and it does match up to the same size, but it fits her a little bigger than most of that stuff does. May be the shape. It used a little less than 2 balls of the verigated (We'll call this Color A) and probably less than half a ball of the solid color (So, that'd make this Color B), plus five 1/2" buttons.
Anyway, the pattern is super easy. It uses exclusively single crochet (and chain) except for the flowers.
Here it is:
Guage with Cottontots yarn on a 4.75mm hook is 9 stitches and 10 rows per 2" in pattern.
For Pattern Ribbing, crochet into ONLY the back loop of each stich in the previous row throughout garment. (Excluding flowers and edging.) You're crocheting sideways, sort of. Here's a diagram of what the completed piece, before stitching, will look like.
With Color A, chain 36.
Turn, sc in second chain from hook.
Sc across row.
Turn, then sc into only back loop of next stitch.
Continue across row.
Complete seven rows (total, but not including chain row) like this. You should end at the "top" edge.
At end of seventh row, instead of chaining to turn, chain 15.
Turn and complete seven rows in pattern on 49 stitches. This should put you back at the bottom edge again.
Begin another row, but only sc 32.
Turn, and complete a total of 19 rows (including the one you just completed).
Chain 18 at end of 19th row.
Turn, complete 7 rows total on 49 stitches, again ending at the bottom edge.
On the next row, sc only 35.
Complete 25 rows on 35 stitches, chaining 15 on last row.
Complete 7 rows at 49 stitches, ending at bottom edge.
Sc 32 stitches for 19 rows, chaining 18 on last row.
Complete 7 rows at 49 stitches, ending at bottom edge.
Complete 16 rows on 35 stitches.
Switch to Color B. Complete 5 rows on 35 stitches.
Finishing: Sew tops of straps together. (I'm terrible at this, which is why there are flowers there.) Sc edging with Color B around all edges. For button holes: Along the edge crocheted with Color B, during edging, sc 3 stitches from bottom edge, *chain two, sc into third stitch from last sc, sc 4 more stitches (5 stitches total). Repeat from * three more times. Chain two, sc into third stitch from last sc, sc one more to bring you to edge of row.

These are the buttonholes, up close and personal, just in case my instructions weren't clear.
For flowers, if you need or want them: Chain 6, sc into first chain, Dc 1, then sc 1 into ring to complete first petal. Next four petals each consist of 1 sc, 1 dc, 1 sc into ring. Join with slip stitch to first sc and clip, leaving enough tail to sew. Make two. Leaves: Chain 4, turn, sc into second chain from hook, dc into next stitch, then chain one and clip, leaving tails for sewing. Make 2.
This is such a great basic pattern! You can do all sorts of things with it. Fancy up the edging with scalloped edges around the neck and bottom edges. Put the flowers on the front. Heck, put any darn thing you want on the front! I may have gotton the buttons wrong, I really don't know. (As far as which side is supposed to overlap which other side for girls clothing vs for boys clothing...) The only thing which determines whether the off-center buttons are on the right or left side is which direction you work your edging. So, if I did it wrong, you can fix it.

You can make the shirt longer by just making the rows longer, or by adding decorative longish edgings. (I'm working up a pattern that includes a curled sc edging during construction instead of finishing, and I think it'll be really cute.) Plus, it's cotton, so WILL block pretty well, or shrink a little if you need it to. You could modify the pattern nearly endlessly to substitute lighter or heavier yarns or to make bigger or smaller sizes. This would even be an EASY pattern to modify to adult sizes!
Note: I never blocked this. And I've never washed it. I honestly don't know what will happen when I do, as I've never worked with this yarn before. But, in all honesty, it's too big for my daughter right now, so if it shrinks, I won't be too upset. However, I could anticipate some issues with the button holes after washing, and would recommend being gentle while washing and drying. Don't remember what the care instructions on the yarn label were, but I assume laying flat, being sure the button holes aren't shrunken, is a good idea. And hey, a failed experiment using cotton yarn always equals extra dishclothes!
So, I hope my first attempt at a crochet pattern isn't completely lame, and I hope second attempt at a tutorial is less lame than my first. Thanks for reading!