You can use any wire you have. Large diameter wire will be more difficult to manipulate, but will increase the rigidity of the product You can combine colors and beads sizes as you like. materials I ...

Soft copper wire : 20 gauge ( wire diameter 0.8mm ) : cut the segments 1.5cm ( 0.6 inch) , 3cm ( 1.2 inch), 4cm ( 1.6 inch), ...