This "Dream House" project is a super-fun way to attack additive area concepts. This resource is aligned with Common Core standards for grade 3, but would work well in any classroom that is exploring area.
Common Core Alignment:
CCSS.Math.Content.3.MD.C.7d Recognize area as additive. Find areas of rectilinear figures by decomposing them into non-overlapping rectangles and adding the areas of the non-overlapping parts, applying this technique to solve real world problems.
This fun freebie incl