Well, if you mean you want to make a light sabre you can upgrade - you'll need the artifice crafting skill and get yourself a schematic for one - either by buying one from the market or by doing some treasure hunting missions, grade 2 I believe, schematics will drop randomly from these missions and do so very frequently. It's usable at level 20.

This will give you an orange bordered item with no upgrades, an empty shell.

With artifice you can craft enhancements and hilts to put into it. You'll still be missing a mod, you'll need to buy these from the market, get one as a mission reward or trade in some commendations.

You could of course, with artifice start upgrading your hilt and enhancement slots in any orange bordered sabre you already have.

Building your custom lightsaber is pretty much the same as building any custom piece of armor. If you have an orange or purple item / shell, using control + right click will open the customization window where you can replace and swap mods, enhancements, augments, armorings, barrels and hilts.

if you keep all the component up to date, you can level from 1 to 50 and still keep the same appearance.

but how do you come across the custom shell... I am so confused when it comes to this system some times...

The Lightsaber you got on Korriban should have been a custom quality item. So you should have one already. If you have one you can ctrl+right click on it to open the modification window where you can change out the different modifications. For a lightsaber those are Color Crystal, Hilt, Mod, Enhancement and Augment. There are several places you can find them. Quest rewards, the GTN and Modification vendors, the most common ones being the ones that use planet commendations and are located on the Fleet among other places. Hope this helps.

They're also for sale on the galactic trade network. All orange border items can be customized, use the filter options to sort so only orange shows.

Some weapons vendors on planets may sell orange too. And check commendation equipment vendors on the fleet dock.

The Lightsaber you got on Korriban should have been a custom quality item. So you should have one already. If you have one you can ctrl+right click on it to open the modification window where you can change out the different modifications. For a lightsaber those are Hilt, Mod, Enhancement and Augment. There are several places you can find them. Quest rewards, the GTN and Modification vendors, the most common ones being the ones that use planet commendations and are located on the Fleet among other places. Hope this helps.

Augment slot is only on the item if you A) add an agument slot kit to the item, or B) get a critical success crafting it.

The basic modification slots are Hilt, Mod, Enhancement and Crystal for lightsabers.

 

Augment slot is only on the item if you A) add an agument slot kit to the item, or B) get a critical success crafting it.

I forgot to put crystal in there, thanks. Good point about Augments, but you can have them on lightsabers so that's why I mentioned them.