Sketch a cube using intersections
Start with 10 mm spacing. Pick an intersection for the back corner of the top face. Follow the sloping lines two intervals down-left and two down-right. An interval runs from one intersection to the next. From each endpoint, follow the other slope for two intervals to close the diamond. Drop two vertical intervals from the left, right, and front corners. Connect the lower front corner to the two lower side corners. Try wider spacing if you need room for labels.