The bows could be different lengths. Measure between the mounting holes straight across, and then measure the bows the same way. They also could be color coordinated. The rubber grommet that holds the end of the bow could be colored to match one end of the bow. Check for tell-tale paint residue on the grommets and the ends of the bows. If you get the bows in their correct places, hold them vertical and measure between the bows to the center of the bows and add your seam allowance (usually 3/8 to 1/2 inch ) at each end. In other words, if the distance between the vertical bows is 15" , your fabric should be cut at 16 " assuming a 1/2" seam allowance. Be aware that at the ends of the bows you will need to curve the fabric to make up for the curve of the roof line whre it changes from horizontal to vertical. If you have never done this before, order a headliner to match your car. Good luck. Try www.kanter.com for headliners. Good luck.
Never did it before,car Interior is something I always
wanted to try. I worked at Woolrich back home, so
I do know a little sewing but not this kind. This
car is a basket case so it makes me even more into
it just to see if i can