Gigalith should be a well used pokemon, but due to its many weaknesses and the fact that there has been an increase in Konjondo leads or Mienshao leads it hasn't been used often. High-Jump kick is one of the main problems why Gigalith hasn't been used. High-Jump kick gives 4x damage instead of the regular base 2x damage to Gigalith,but there is a set that can semi counter it.
:Sand Strength or Sand Force(DW)
One fun fact about Gigalith is that it has no affect to the OHKO moves Horn Drill, Fissure, Guillotine,and Sheer Cold. As you should know, Sturdy assures that you cannot get OHKO from full health. Sand Strength or Sand Force increases all of Gigalith's Rock,Ground, and Steel type attacks and also gives invulnerability to damage from Sandstorm to Gigalith.
Gigalith doesn't actually have well proven sets except if you make a custom one.
Adamant Nature Gigalith
EVs: 252 HP/4 Atk/ 252 Def
This set is used when leading with Gigalith. Putting the main portion of your EVs into a tankier set is necessary to start off. Putting the 4 remaining EVs into Atk is also useful since your adding to its enormous strength. Gigalith w/o the 4+ Atk EVs already has a base 300 attack with its adamant nature which gives 10% more Attack then your usual neutral natures. Stealth Rock starts off the beginning of a battle, so that this way you have an advantage when your opponent switchs.(Especially when they run a Baton Pass Set.)Rock Blast is just an amazing move. It counters and overpowers substitute sets and demolishes Ninjask and Shedinja leads.Protect is your counter towards Konjondo.(semi counter).Protect protects against High Jump Kick and brings Konjondo to nearly 50% health. Protect will also apply to all 2x and 4x attacks too Gigalith. However, protect can't be overused(which sucks :o). Toxic is great if you still want to use Gigalith later on. This way you can poison your opponents and put alot of damage over time. Explosion is great if you want to just end it now. Explosion, however, got nerfed so that it doesn't lower base defense. Explosion still does a great deal of damage and with Gigalith's 300+ base damage it should be a sure-kill and if not, should be at least at 25% health.
Careful Nature Gigalith
Ability: Sand Force or Sand Strength(DW)
EVs: 252 HP/ 4 Atk/ 252 SpD
Item: Leftovers/Chesto Berry
This custom set is used for and against Sandstorm and or Trick Room sets. Careful Nature increases Gigalith's Special Defense while lowering its Special Attack. Sand Strength will increase Gigalith's base or physical attacks's strengths when in a sandstorm. Leftovers is best when your in a Sandstorm team and Chesto Berry is best when in a Trick Room team. Curse increases Gigalith's Attack and Defense so that now you'll have a ridiculously high SpD and Defense. When Sandstorm is activated you'll be able to do a lot of physical damage with Rock Slide and Earthquake. I chose Rock Slide over Stone Edge because of the fact it has more PP and it gives the chance to make the opponent flinch. Earthquake was chosen just because it was an overly awesome ground type move which receives a lot more power with Sand Force or Sand Strength's ability. Rest was chosen because after using Curse, you'll be able to have full HP and be able to take more damage from the physical or special side of attacks. This set displays Gigalith's abilities to the fullest. This set is probably the most effective because it uses all of his stats to it's full potential.
PS. Please tell me how to put a picture of the pokemon on these POTWs :O I'm really getting noobish at this now.