In order to build a lightsaber, you will need a few key ingredients. Here are some links that can help you with that.
http://starwars.wikia.com/wiki/Lightsaber
http://starwars.wikia.com/wiki/Lightsaber_crystal
Some crystals can work together, some cannot. Be careful when choosing which ones you wish to place in the saber. Rare or powerful crystals will need approval from the moderators.