Make a T-tunic
For more advanced instructions (it'll fit better, but take a bit longer), see:http://www.reconstructinghistory.com/beginners/StLouis.html
Of course t-tunics can be as complicated as you want them to be, and can fit quite tightly. But even the more interesting t-tunics from the middle medieval period (12-14th C) are simpler to picture for people with good spacial skills than late period garb - it's still just rectangles and triangles, just more of them.
T-tunics are extremely ecomonic on material usage. If you can get 150cm wide fabric, normally twice the desired length of the tunic plus half a metre will give you a good tunic.