|Like other fellow units of the myrmidon archetype, Saber's average Attack but other fantastic stats stats all-around make him a prime candidate for inheriting Wrath 3. Not only does said skill add a flat 10 damage to Saber's special skill activations (making up for his otherwise middling damage output), but its out-of-combat, cooldown-lowering effect makes it easy to activate said special, especially if Saber needs to retreat from enemy range. Other than Wrath itself, Saber's stats, weapon, and skills come together to create a surprising reliability, sturdy build, capable of winning out of most forms of melee combat.
Saber's native Slaying Edge+ decreases cooldown count by 1, making it even easier to fire off a Wrath-powered special. Wo Dao+ is a nice alternative that further adds 10 true damage to Saber's specials, giving short but weak specials like Moonbow significantly more bite. However, Slaying Edge+ is generally more reliable with Wrath and comes by default, whereas Wo Dao+ is rather expensive in comparison as it must inherited expensively from another 5-star rarity unit. At any rate, both weapons should be Speed-refined to allow Saber to keep up with other faster units, create doubles of his own, and make up for his relatively low HP. A Defense refine is also excellent if you want Saber to excel in melee matches.
While Wrath is the bread of the build, Saber's chosen special is the true butter. Moonbow is preferred for its short cooldown of 2 as well as generally benefitting more from the additional 10 damage than other specials. Bonfire gives Moonbow fair competition, however, as its cooldown becomes 2 after welding Slaying Edge+ and deals around 18 damage at base (assuming neutral, unrefined Defense) compared to Moonbow's weaker, less consistent, but faster performance.
The A slot skill further improves Saber's fantastic melee capabilities. Fury 3 is easily acquired from any 4 star Hinata and improves Saber's balanced stats and performance all-around. Furthermore, Fury's self-inflicted recoil after each skirmish, combined with Saber's nice bulk, makes it very easy to put him at Wrath range (75% HP or below). Though Steady Breath is a significantly more expensive alternative, it should also be considered for its double special charge in Enemy Phase. Said effect makes it insultingly easier to proc Wrath-powered special while opening up a few more options for Saber in terms of specials, especially the significantly more powerful Ignis and Aether.
Reposition and Draw Back are standard positional skills that can help other Saber and his teammates avoid enemy range while having offensive applications. Saber has a lot of options as far as Sacred Seals are concerned: for example, Close Def 3 further improves Saber's performance against melee units, especially against the likes of opposing sword units as well as Res-hitting dragons such as Fallen Robin. Quick Riposte 3 gives Saber a guaranteed counterattack in enemy phase when near full health; although it sounds silly on a Wrath set, it generally gives Saber more options when he's not quite at Wrath range. Other Seals of note include Speed +3 and Attack +3 for flat but considerable stat boosts, as well as Quickened Pulse if an initially-charged special is appealing.