What you're gonna need are:
1 necklace wire with screw-clasp *
~40 pearls (with a diameter of at least 1,5 cm)
~40 matching seedpearls **
*These can be found at e.g. Näpsäkkä in the colors blue, gold, black, silver, red, pink turquoise.... I love using them, since the wire makes the pearls fall nicely around your throat, and the lock is already prefitted to the wire.
** Make sure these are at least size 8/0, as smaller usually have hole that won't fit around the wire I've used here!
String the pearls on in any order you want them to be - here I put a seedpearl between each large pearl - then close the clasp onto the wire with a straight-nosed plier.