Hi Nick,
You're on the right track, but alas, it's not reportable, so instead, I invite you to consider our Capacity Charts solution, which includes "all the math, in graphical form" for Capacity, Planned, and Actual hours (twenty ways to Sunday) rolled up correctly at a Daily, Weekly, Monthly, and Quarterly level (even for Tasks that span across Months).
Alternatively, if your timeframe more near term, you might also want to check out the built in Workload Balancer, which might be sufficient for your requirements.
Regards,
Doug