Try this sheet below. Instead of choosing somewhere in school like it suggests, choose some other features. These could be in your garden, at park etc.
Furthermore, if you do not have a tape measure, be creative, can you measure the features in other ways e.g strides, feet, hand widths etc. Remember to keep the measurements across the different features consistent.
Try this mathematical art, I promise it is simple maths. Look at the Celtic Knotwork Powerpoint below and follow the sheet to help create your pattern.