Ironclad

Ironclads are often found on the front lines of battles, standing firm and unyielding against enemy attacks. They are the guardians of their party, protecting their allies from harm while absorbing blows that would fell lesser fighters. Their armor is not only incredibly strong, but also finely crafted and personalized to their individual specifications, allowing them to move with surprising grace despite the weight and bulk of their equipment.

Ironclads are often stoic and determined individuals, willing to endure great pain and hardship in order to protect their allies and achieve their goals. Their will and armor is constantly put to the test. They may not be the most glamorous or flashy fighters, but their dedication to their craft and their unbreakable resolve make them a valuable asset to any adventuring party.

Custom Layers

At 3rd level, when you pick this fighter archetype, when you take a short or long rest, you can attach or detach additional metal plates tailored to work with various armor. These are heavy metal pieces that slow you down, but provide good protection. You can equip a number of plates equal to your proficiency bonus. Each plate provides a +1 bonus to your Armor Class, but decreases your movement speed by 5.

Armor Adept

Also at 3rd level, training to make the most out of your armor, you are a master of battling in normally potentially obstructive armor and are quite the athlete from the strenuous equipment you carry regularly. While you are wearing armor, your movement speed increases by 5. 
When an allied creature is within 5 feet of you and a creature attacks it, you can use you reaction to attempt to block it and all incoming attack rolls, until the start of your next turn. All attacks involving an attack roll directed at that creature are redirected to you instead. You cannot stop protecting a target in this manner unless you are incapacitated. 

Juggernaut

Starting at 7th level, when you start moving, little can get in your way. You ignore magical and non-magical difficult terrain and are immune to being stunned. If you move in a straight direction for 15 feet or more during your turn, any large or smaller creature is knocked out of your way (to the left or right of you, DM’s discretion) and cannot make opportunity attacks against you until the start of their next turn.

Unwavering

At 10th level, when you brace to defend, little can get through. When you take the dodge action, you also gain resistance to all damage until the start of your next turn. This effect does not apply if you dodge using anything other than your action, such as dodging with a bonus action through a rogue’s cunning action.
When you are reduced to 0 hit points, you make death saving throws as normal but do not fall unconscious.

Spellbreaker

Starting at 15th level, you have been in countless battles, and you know exactly how to make the most of your armor against spellcasters. When a creature targets you with a spell, it must make a spell attack roll against your Armor Class, unless the spell itself requires a spell attack roll normally. If it misses, the spell fails to affect you, and if it hits, the spell proceeds to work as it does normally. If you resist a spell in this manner, the spell slot is not expended. 

Final Stand

At 18th level, you fight with everything you have when down to your last breath. When you are reduced to half of your maximum hit points, all attack rolls made against you are made with disadvantage, and you have advantage on all saving throws. While in this state, you also cannot be moved against your will.

Additionally, you cannot be knocked prone against your will.