Draw a rectangle 18″ high by 13.5″ wide.
Make a mark 9.5″ from top right corner.
Make a mark 15″ down right side.
Make another mark 8.5″ down left side.
Draw a line 8.5″ down from the top mark. Continue drawing down to the bottom, curving out to the bottom left corner.
Draw a line form this bottom left corner curving up to the 15″ mark on the right side.
Wirte on the right side “place on fold”. (that 15″ line)
Cut out this piece. It includes seam allowances.
You hem the sides and turn down the top enough to put a ribbon or strap of material through.
Wasitband ties are 4″ by 48″(or so) long. If your fabric was 45″ wide, that’ll do. Attach that to the waist section, matching middle of halter with middle of strap.