Hey Miguel,
The report must be informative whether it is of 3, 5 or 10 pages. There is not set format for these reports but you have to order them correctly so that the manager gets a clear idea of everything about the on going projects. One should order the reports like this :-
1). The project should be decribed clearly on the start of the report. What is the project about, what is required to complete the project, what is the deadline of the project, what is the amount of man hours would be required to complete the project, etc etc.
2). Next you can do create a profile of all the resources you need to complete the project. The profile will include the skills, the experience, the degree, the areas of expertise a resource has to have to be the part of the project.
3). Then with the help of calendars, you can show the way you have scheduled the resource on the project. This calendar will also include whether a particular resource is working on his full capacity on the project or not.
4). Include a utilization report to show how the resources are being utilized. The report can also show that resources over utilized or under utilized. Also you can give a forecasting report on whether the project will require more resources or not.
5). Finally a financial report, so that the managers is also aware of the financial aspects(billing cost, cost rate, revenue generated, losses) of the ongoing projects.
You can manage your projects and resource by eResource Scheduler that has detailed niche reporting features which help you to generate real time reports for in depth information about your projects.