See attached screenshot for a better explanation.
The lines drawn around where I need the extrude are done in 3D sketch with weldments for the tubing. I've managed to do this before to get an extrude of a few mm thick without any issues, except it was all straight lines and no curve in the glass. This time, there is a slight curve, and it doesn't want to do what I need it to do.
It's essentially a slightly curved windscreen. Are there ways around this problem, or any better ways of modelling a curved windscreen given I already have the base and roof to attach it to?