Here's a little tutorial on how to modify a plain t-shirt, inspired by this one.
What you'll need:
- a t-shirt: a loosely fit one will do but - as a rule - huge t-shirts are more fun (as you have more room for improvements/changes/customizations);
- fabric shears
- needle and thread (or, if you prefer, a sewing machine)
Step 1: the neckline
Put the t-shirt on a flat surface, then start cutting out the collar, to create a new neckline: cut two slits about 2 cm from the collar (from both sides), then cut out a circle. Flip the tee and do the same on the back side.
Step 2: the bottom hem
Try your shirt on and mark the desired lenght. I decided to create a curved hem, to make it more feminine: to do it, you'll just need to cut an half-moon shape on the bottom line of the t-shirt.
Step 3: the shoulder strap (optional)
Just to add a little twist, I decided to sew a ribbon as shoulder strap. You'll just need to measure the required lenght with the tee on, and mark the place to sew the ribbon. After sewing the strap, you can also add a little bow on the front side.
Don't throw away the scraps, use them to make a fabric necklace!
Some resources on t-shirt surgery: