Hi Mollie, try the following and see if this is what you were looking for…
In an Hour Report, click on the Hours column (am assuming you are looking for actual hours -- this column is automatically added to an Hour Report when you start one), and choose “Summarize this column by:” --> Average.
For Groupings, select Project --> Name and then Job Role --> Name. Also be sure to add any Filters needed, so as to reduce the amount of data returned – e.g., Project Actual Completion Date.
Then, go to the Charts tab, and select either Column or Bar Chart. If selecting Column chart, the Left Y Axis would be Hours --> Hour and the Summarized by would be Average. The Bottom X Axis would be Project --> Name. Then toggle Group Columns On, and Group Data by Job Role --> Name. I would suggest choosing the Stacked Column option. Hopefully, the resulting chart is what you were looking for.