Hi @cammipatterson what a great starting project!
I haven’t made an above the knee t shirt dress but I have used the metro pattern to make a t shirt maxi dress for my teenage daughter.
What I did was measure where she wanted her dress to finish and then I made the adjustment to the pattern by adding the amount of length and cutting through the pattern pieces between the hip and hem. I did this on both the front and back pieces and then I lined them both up to make sure they would be equal.
Some points to remember, the hem is not included in the final measurement so when you measure the pattern you have to remember to make the length to accommodate the hem. The bottom of the t shirt may need to be slightly a lined – just slightly. And this will allow for movement and less restriction around the leg area.
Other than that it is very straight forward and very quick to make. Ideal for the hot weather and if they need to, add leggings or make it an extra long t shirt over pants if it gets a bit chilly.
My daughter’s maxi is now too small as she has gone through some very significant development being early teens. But come summertime (in Australia) no doubt it will once again become a wardrobe staple.
Hope this is helpful
Tamara