This lesson launches the discussion of area into surface area and volume, with the specific goal of contrasting their meanings. Essentially, after students build a prism that has a net on the outside and yet is filled with unit blocks, they are prompted to make sense of the difference between the two concepts.
Please note, this lesson is designed around unit cubes that are 2 cm each, as well as a 4 cm x 6 cm x 8 cm block (made easily from 2x4's - but only the unit cubes are critical). If you have unit cubes of a different dimension you would simply need to adjust the dimensions of the net.
This is one of 12 lessons in my "In and Out" unit that targets area and volume for 7th graders in the advanced track. The goal of the unit is to build understanding of why the formulas for area and volume work, such that if students forget the formulas, they can cognitively reconstruct them on their own.