Build It Up! is an engaging activity that integrates science with mathematics through a process that encourages problem-solving, principles of design, creativity, and developing a sense of one's community. This activity, aimed at third- and fourth-grade students, allows students to use manipulatives to design, construct, and test buildings they develop. It also provides students with opportunities to collaborate with their peers and reflect on their understanding of science process skills and principles of design. (Contains 8 figures and 2 tables.)