How to construct ROC curve for MNIST using Pegasos.(Primal Estimated sub-GrAdient Solver for SVM) algorithm?

Hi guys, I'm actually having a trouble with constructing ROC curve in Matlab. The idea is that i use the pegasos algorithm to find the equation of the linear separator hyperplane that separates the MNIST data. And i need to construct a ROC curve for the classifier performance, but until now i haven't found the way to make it happen. I've seen that it needs the scores in order to plot the ROC curve, but how can i find that scores? Can anybody please give me any idea? Thanks in advance :)