Is it pointless very fish friendly no need to zero the scales to take in to account the weight of the sling ideal for roach,rudd,perch crucians etc. No need to wash it bin it at home after use.
If you do want to make your own go down the local market and buy enough nylon theres plenty of choice available in colour and denier. Buy 2 "D" rings from a shop like Millets or a camping shop. Then cut out the size and shape you want and sew together on a machine. Its almost a D shape you want.