I found a book called 'Evaluating the impact of leadership development' by Patterson, Stawiski, Hannum, Champion and Downs really helpful when I did something similar last year. I got hold of a copy on Amazon.

be conscious that if you didn't define what you planned to measure when the workshops were designed the levels 3-5 of Kirkpatrick (there is 5th return on expectation) may be difficult to measure. however it's worth looking up a website called training check it is software that specifically measures training evaluation and has a massive bank of stock questions, organised by Kirkpatrick that allows you to create online surveys before, during & after workshops. i use it for all my programmes & it saves me hours of time.