There are so many activities that help develop an understanding of area as well as build up number sense in the process. Check out YouCubed's How Close to 100?
The good folks at Khan Academy provide some great videos to support your understanding, as well as some questions to practice with. Here is a good link about Area and Perimeter
to get started with. Also worth checking out is a series of activities from NRich Math
. This site also has a variation of How Close to 100 called Dicey Perimeter,Dicey Area