I've been on a t-shirt making spree (I have no t-shirts to wear now I am on hols). The pattern is the one I mentioned a few posts back, downloadable from a website How to Fashion Design with Bob Martin.
The interest is in the back and underarm area, where the gussets give the t-shirt its shape. It is very similar to a Vivienne Westwood Anglomania t-shirt I found at a sale a few years ago and wore to death (and have unpicked for remaking in the near future) so I am sure to get lots of wear out of this one.
The first version is in a lovely and soft, drapey green rayon spandex jersey from Denver Fabrics. Unfortunately, it was so drapey it got bigger and bigger and bigger... so I'm about to unpick the side seams and take off an inch on either side - and take quite a bit off the sleeves.
I've also made up a light grey version with dark grey contrasting gussets. For this one I changed the neck to a scoop neck and took in the sides by 1.5cm and the shoulders by 2cm. I'll get some better photos when I see some sun.
And... a plain grey one is about to be finished.
When I did a muslin for this top, the jersey was less drapey and it made very unnattractive back arm pouches. I'm not sure this would be a problem in a more fluid jersey, but to make sure I took out some of the volume of the lower gusset. Original gusset pattern piece: