Hi Martha,
I presume you're planning to export a report for the non-Workfront users. Assuming they just want to see the number of unassigned (i.e. available) hours per person you might even be best to do a screenshot or export from the Resource Planner which can show you the Available Hours, Planned Hours and remaining "Dif" (difference) and percent allocated. This will give you the most accurate values because it takes into consideration only the hours assiged for each day, regardless of the start/end dates of the tasks. If you were to go down the path of writing your own report you are going to run into inaccuracies if you have tasks which span between weeks. If all of your tasks only stay within one calendar week then you should be OK proceed with an Assignment Report. It would be best to filter it based on task planned start date greater than or equal to $$TODAYbw and task planned completion date less than or equal to $$TODAYew. If your people also work on Issues then you would need to add similar filter conditions for those. You'd then want to use matrix groupings to group by Assigned to Name (and possibly by Project if you want that). You'd need to set the Assignment 'Planned Hours' field to SUM then you should be done basically. Hope that helps.
Regards, David Cornwell