Measure around your bust and multiply by 1.5 then divide by 2. Add 1" allowance.
Use this last measurement to draw the top of the dress.
Measure the length of the dress from collarbone down to kneecap or floor for maxi dresses. Add 2" seam allowance
Use this measurement to draw the sides of the dress.
If you decided to make your dress an A line shape (figure 1) you need to add 1/2" to left and 1/2" to the right of the bottom line of the pattern. Then modify the size to meet the enlarged bottom and the top.
If you decided to create a concave in the top (figure 2), find the middle of the top and mark 1" below the middle. Join the left and right of the top through this point.
Measure 6" down and 2" in from the top on both sides and draw a curve for armholes.
I advise you to use the A line shape pattern as it's easier to sew and hem later on.
Cut and sew the fabrics
Cut two pieces of fabric to match the pattern and place them right sides together.
Place the pattern on and cut out.
Pin the sides of the fabrics and sew with 1/2" allowance. Finish with a serger or a zig zag stitch. (I didn't make a pattern in advance,, I worked straight on the fabric so on this image you won't see the armholes)
Hem the dress with a narrow hem.
Finish armholes with bias tape (I made my own in the same fabric as the dress. Check out these tutorials if you decide to make your own bias!
Finish the dress
Finish the top with a serger or a zig zag stitch
Fold the top in about 1", pin and sew to create the casing for the shoulder straps.
Make a long strap. Make the straps long enough to use for shoulder straps and the waist tie.
Thread the strap through the dress casing and tie on one shoulder.
Sew two tiny loops on the sides of the dress, about 3" down the armhole, to secure the waist tie when wearing.