Answer for D&D 5th Edition.
- Am I allowed to play as Animated Armor?
- And if "yes" how would I go about making such a character stronger?
Answer 1 to Question 1
You'll have to work with your DM, and perhaps consider a Warforged character.
There is no Player Character Class in the Players Handbook with the description of animated armor you called out, but the Warforged seem similar. During your discussion with your DM, explore how a Warforged character (outlined in a Wizards of the Coast Unearthed Arcana Article) might fit your idea. This race is for the Ebberon setting, and is ported in from earlier editions of D&D. Now that the Wayfinder's Guide to Eberron is published, it may fit better.
The Warforged were made as the ideal soldiers to serve in the devastating Last War. Although they are constructs, they have much in common with living creatures, including emotions and social bonds, and perhaps even souls.
Ability Score Increase. Your Strength and Constitution scores increase by 1.
Size. Warforged are generally broader and heavier than humans. Your size is Medium.
Speed. Your base walking speed is 30 feet.
Composite Plating. Your construction incorporates wood and metal, granting you a +1 bonus to Armor Class.
Living Construct. Even though you were constructed, you are a living creature. You are immune to disease. You do not need to eat or breathe, but you can ingest food and drink if you wish. Instead of sleeping, you enter an inactive state for 4 hours each day. You do not dream in this state; you are fully aware of your surroundings and notice approaching enemies and other events as normal.
Languages. You can speak, read, and write Common and one other language of your choice.
This gives you a point of departure in your discussion with your DM, and could apply to any class in the Players Handbook. Keeping it a secret might not be possible, if you take that option.
Answer 2 to Question 1
Since you may be referring to a construct from the Monster Manual, Animated Object, (p. 19-20 of MM; p. 9 Basic Rules, DM) then you need to proceed as follows:
Discuss this in detail with your DM, since you wish to create a monster as a playable character. In all editions of D&D this can be fun, but it brings with it some risks of not fitting with the rest of your party, and balance issues run amok. In the DMG Chapter 9, the Dungeon Master's Workshop, some tools are available for you both to work with.
In order to "make it stronger" (I presume by that you mean gain capability as you progress in level) apply the same XP goals as other characters for levels 1 through 20, then agree on the special skills and traits that accrue as levels progress: you'll want to fit in special abilities at levels 2, 3, 5, 6, 10, 14, 18, and maybe 20. (Or, drop one of the later ones, that may be a bit much ...)
By level six, your homebrew character should look something like the stats of "Animated Armor," which has six hit dice.
Animated Armor (Medium construct, unaligned)
Armor Class 18 (natural armor)
Hit Points 33 (6d8 + 6)
Speed 25 ft.
Abilities: STR 14(+2) DEX 11(+0) CON 13(+1) INT 1(−5) WIS 3(−4) CHA 1(−5)
Damage Immunities poison, psychic
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, paralyzed, petrified, poisoned
Senses blindsight 60 ft. (blind beyond this radius)
Passive Perception 6
Antimagic Susceptibility. The armor is incapacitated while in the area of an antimagic field. If targeted by dispel magic, the armor must succeed on a Constitution saving throw against the caster’s spell save DC or fall unconscious for 1 minute.
False Appearance. While the armor remains motionless, it is indistinguishable from a normal suit of armor.
The armor makes two melee attacks.
Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., one target.
Hit: 5 (1d6 + 2) bludgeoning damage.
This suit of magically animated plate armor clamors as it moves, banging and grinding like the vengeful spirit of a fallen knight.
Conclusion: Stealth checks at disadvantage, if even allowed. Good luck keeping this a secret.
- How much stronger can you make this? Look at all of the immunities. Perhaps look at resistances or saves with advantage.
- How playable is this? Look at the penalties to Wisdom, Intelligence, and Charisma. During character creation, discuss with you DM how to adjust this to make the A.A. more playable.
These strengths and weaknesses need to be addressed before you make it into a playable race.
Working with your DM is critical for two reasons:
- Retain balance within the DM's campaign
- Your indication that you might want to keep this a secret, presumably from the other players.
Answer to Question 2
This answer depends on how you and your DM answer Question 1. Your decision on a Warforged character, or a playable suit of animated armor (monster/construct) as a PC will result in a homebrew character. Any homebrew (which can be great fun!) must (I repeat must) be compatible with:
- your DM's campaign
- your DM"s world
- the players at your table
This takes us back to answer 1:
Work with your DM to see how you can fit this idea into his campaign.
Warning: if anyone succeeds in giving your character a heart, you may turn into a flesh and blood human being! Be wary of picking up the wrong magical axe, young girls with dogs, lions, and scarecrows. :-)