Go ahead and lay out the side triangles and corner triangles (corner triangles not pictured here). Don't worry that the triangles seem a little large...you can trim them later.
Next you'll sew the individual rows together. Each block in the four block quilt will have 5 rows. The single block quilt will have 11 rows to sew together. For the single block quilt I sewed six rows together; I then sewed the other five rows together before sewing the two halves together into one piece. After adding each row, press to one side.
Now measure your topper through the center (in each direction) to find the measurement to cut your border strips. This measurement should be close to 18". Lay out your border strips and the remaining four colored squares. Sew the left and right border strips to your quilt, pressing towards the borders. Then, sew the squares to the left and right sides of the remaining two border strips. Again, press towards the border fabric. Then, sew the top and bottom border fabric strips to the top and bottom of your quilt. Press towards borders, and you're done!
Now you're ready to layer, quilt, and bind...unless you want to add an additonal outer border (I'm going to wait for yardage to come out in both of these lines so I can add a border and binding from the line).