Is it possible to create a spreadsheet that shows gaps between certain dates?

I am creating a spreadsheet with VBA functions for work, I have a basic idea on VBA and can get it to do most things (after a good while searching for help and adjusting code etc) however before i even start with this challenge I need to know if its possible.

What I need my spreadsheet to do:

We have a larger number of staff (for this example we will say 100 to keep it easy) at work and we carry out different roles throughout the year and need to keep track of who is where and for how long for example:

Role 1 could start 01/01/2017 and have 20 people and end 05/05/2017
Role 2 could start 01/01/2017 and have 60 people and end 10/05/2017
Role 3 could start 01/01/2017 and have 20 people and end 31/12/2017

Role 4 could start 11/05/2017 and have 80 people and end 31/12/2017

In this scenario 20 people do not have a role between 06/05/2017 and 10/05/2017

Is there a way for this information to be flagged up on screen telling me if there was anyone without a role in 2017 (when these dates are as well would be great but not essential)

I hope this makes sense. Any help or other solutions would be great.

Thanks
Garry