I love these kinds of tops, but the prices are such a rip off. Half a metre of light cotton ($2 CDN) and a metre of lace ($1.50) later and I got this:
Lace Detail and clevage shot:
ANNNND stupid pouty face pose :
Colour's a little wonky, my camera doesn't agree with the fact that my room's orange and my hair's purple ^_^
Okay these are basic instructions and I'm gonna assume you know how to use a pattern and have some experience sewing tops.
The pieces are more or less to scale. the waistline should be an inch or two larger then your natural waist and if you're not putting in a zipper (i didn't feel the need to) make sure it's big enough to squish your boobs through. The top edge of the front and back pieces should measure about an inch larger then your ribcage just under your breasts (where the bottom of your bra is).
ALWAYS CUT THE PIECES TOO BIG!!!!!! Baste everything, and take it in as needed.
Draft the pattern and cut out your pieces. Sew the back top to the back piece.
This is the hard part: the bottom edge of the top triangle thingies has to be gathered to fit under your breasts. Stitch veeery loosely along the bottom edge of each piece and gather it in the middle a little bit.
Pin it to the front piece and hold it on your body or dress form and make sure it works. *Note* Pin or Baste the front triangle on first.
Baste the sides together and take it in as needed.
Sew everything together and add straps. I didn't include these in the pattern but get creative. I tested this pattern by making a halter top and it worked out great. Finish the raw seams and hem it.
I'll elaborate when I have time, if you're confused about something PM me.