I made this maxi dress from some knit fabric I picked up. I was originally going to make the boho maxi dress but decided I didn't want to have to wear a belt or sash for the waist shaping to look all right so I went with this type of design instead.
To make the dress I used two yards of fabric, and I mean almost exactly two yards! I was getting nervous towards the end because I was afraid I wouldn't have enough to make the straps that wide. I wanted them wide to hide bra straps because I don't like strapless bras, but the dress would look cute with thinner, maybe braided straps too. The fabric was 60 inches wide, and that's how wide the very bottom is, minus seam allowances, so if you want a loose flow-y bottom to the dress you'll need more fabric. If you're shorter than me (5' 8") you could probably cut the dress pieces perpendicular to the selvage instead of parallel and then two yards would probably be plenty of fabric.
The only measurement I used was a width measurement, which I got by measuring a tight tank top (I wear it as an undershirt) as shown:
This measurement should be more than half the width of the tank top because you don't want the dress to be skin tight!
Then I took my fabric, folded with the selvages together, and folded it in half again, so I ended up with two identical, symmetrical pieces for the front and back of the dress. To make the waist shaping I just lined the tank top up on top of the fabric to make the little nip at the correct place, and then cut a straight line down to the bottom of the fabric so at the very bottom it ended up as wide as possible.
I stitched the front and back together at the side seams and tried it on to figure out the length. In the end I had to cut off about 6 inches and hem it to get the length right, and I used those leftovers to make the band at the top and the straps.
The top band and straps are just four rectangles folded in half, two identical ones for the front band and back band, and two identical ones for the straps. I sewed the top band to the dress and tried it on again. I gathered the center at the bust, which added a little bit of shaping. Then I pinned the straps in position and sewed them in.
Now if only spring would hurry up!