Metamagic Dragons

Ok, I want to put sorcery points on a dragons stat block, where would I put that, how many points should I put, wat options would be best for a dragon with metamagic?

I know that this is game breaking, but I don't care about that it's something I want to experiment with, I know dragons are inherent sorcerers, but that is exactly why I'm doing this, I know thus will make them more dangerous to run, I know all if this, so let's ignore those things I help me think of where to put sorcery points on a dragon, I asked Google ai, it said in traits or actions, so plz help me imagine that

Well, in general metamagic works to enhance spells, but for dragons I think we can expand that to magical abilities. 

Since they aren't really casting a variety of spells, it will probably be best to have the options be fairly specific. 

Take the breath weapon. The party knows they are facing a red dragon, so they take fire resistance potions. Red dragon spends 5 sorcery points to change their fire breath to lighting. Boom.

They could spend sorcery points to increase the range or width of their breath weapon. 

Maybe spend 5 points to auto-succeed on getting their breath weapon back. 

Those are some off the top of my head ideas.

In most circumstances, you don't need to track sorcery points. A dragon is presumably going to have a bunch, and encounters generally don't last long.

Just figure out what metamagic-type effects you want it to have, and add the option of doing those to the dragon's abilities. (The dragon need not be restricted to merely the options available to PCs, either.)

Rather than giving them a resource to track, you could just give them an ability that mimics metamagic. Set it up as something like "Once per turn, the Dragon can modify his Breath or a spell he casts in one of the following ways..." Then you can give the effects their own wording and names: Elemental Transmutation, Distant Magic, etc. to create the effects you want him to have.

Or do what I'm doing for Sorcerer NPC stat blocks: Give them X/Day uses of a few Metamagic abilities. No tracking a pool of points, just uses.

Hot take: making a dragon more powerful is in no way game-breaking; they're supposed to be powerful.

To be fair, that might be a question of how you look at the Monster Manual(s).  Personally, I love giving monsters some new abilities to encourage the players to explore the world and learn about things in-game rather than meta-game their way through encounters.  Other groups want to experience the classic monsters in the way that they've been depicted for years, and if you've already established that as your style of play then suddenly throwing out modified monsters is jarring, and you'd at least want to foreshadow it.

But to answer your actual question, I'd suggest what other people have already said:  either modify the ability/attack description with "this creature may choose to...." text, or maybe make it a new feature with "#/day" if you want to limit it.  Using sorcery points just adds an extra layer of complexity onto the same outcome, unless you actually plan to use the other mechanics of sorcery points (like converting them into spell slots), or including some other new mechanic (like tying them into the creature's legendary actions or lair actions).

Sorry for double-posting, I remembered you had also asked about which metamagic abilities, or other features, a dragon could have, and I was going to ask:  what type of dragon are you thinking of using?  And if you're adding metamagic options, are you giving it additional spells or other new abilities to use the metamagic on?  (Or were you also asking for suggestions on that?)

Just to give you an idea of why I'm asking: the party I DM for encountered a green dragon a while ago, which had a few new abilities, including chameleon-like camouflage, tail barbs, and the Stinking Cloud spell.  If it were a red dragon I might have given it the ability to cover itself in flames (temporarily gaining the Heated Body feature) or create areas of flaming ground like the Wall of Fire spell.  BUT if you don't want bigger changes like this, then never mind.

Instead of a #/day (for each or for the lot) you could even do a "recharge" type situation. It's quite a bit more random, but I think the way one would play the MM options under that regime is different from others.