Dungeons & Dragons is like any other hobby, in that it can be entirely too damn expensive. Breaking in to the game isn’t the cheapest endeavor in the first place – if you’re only going to be a player you have it pretty easy, as you only need to get a hold of the Player’s Handbook (and unless you play with a bunch of jerks, one of your fellow players will probably let you borrow theirs to start out) – and if you’re going to be a DM, the costs are that much worse. You have three core books to get at $50 a pop, in addition to whatever supplementary materials you need (including but not limited to: grid maps, miniatures, campaign modules, wet erase markers, mechanical pencils, etc.).
On top of that, there are ever-increasing fleets of supplementary rule books, each containing whole entire slews of new things, be they player character options or new monsters or what have you; if you can think of a type of rule or stat block in D&D, odds are there’s a supplementary book out there that contains more of those things. 5th edition has done players and DMs alike the courtesy of deemphasizing rules, but there is still the temptation to think that because the supplementary rules are official, they are the only additional rules with incorporating.
But they aren’t! You can make up new rules just as well as the people who are paid to do so. This will save you money on supplements, and stretch both your imagination and the imaginations of your players, which is what tabletop role-playing is all about. Here are a handful of pointers for creating new Player Character options for your group:
–Collaborate with your players. It’s worth keeping in mind that D&D is always a collaborative exercise. This may seem like an obvious point, but when you’re in the middle of DMing a session, you’ll be tempted to exert more control over your players than is healthy for yourself, your players, and the fun and well-being of your group as a whole. In D&D, as in real life, you gotta pick your battles.
In terms of character options, this means that if your players pitches you on the idea of a build option that isn’t in the Player’s Handbook, hear her/him out! Talk through what she/he is really trying to do with her/his character, and see if there’s a way to accommodate this within the existing rules. It’s possible that what she/he is proposing is a combination of already existing build options – say your cleric wants to create a domain that has the domain features of the War Domain, but the spells of the Life Domain. This can be done pretty easily, so now the task is to flesh out the in-story justification for its existence.
If you and your player go this route, the most important thing to avoid is letting your player double-dip and gain the full benefits of more than one discrete feature. To return to the above example, you cannot let your player have access to the Channel Divinity features for both the Life and War Domains, or the domain spells of both the Life and War Domains. She/he must choose one and only one to crib from.
Refer to the options in the Player’s Handbook for reference. But, suppose your player wants to invent an entirely new class feature or archetype (meaning things such as Cleric Domain, Wizard School, Barbarian Totem, Bard College, etc.). This is much trickier, since creating a new feature or archetype that has not been playtested by anyone increases the risk of creating broken PC options. If your player is proposing something that you think runs the risk of breaking the game, find a way to compromise (more on this in a bit).
Even so, you can still examine the Player’s Handbook and determine the types of abilities the game considers fair at each level. Within each class, every archetype functions in a manner that is fundamentally the same. Let’s return to Cleric Domains. Each and every Cleric Domain gives the player access to two additional Domain spells at 1st, 3rd, 5th, 7th, and 9th levels. Every Domain gives the player an extra Channel Divinity feature at 2nd and 6th levels, and an additional feature at 8th and 17th levels. So, in order to make a new Cleric Domain from scratch, you must start with this framework.
Deciding new Domain spells is easy, since the spells granted are always tied to the new spell levels the cleric gains access two. So the 1st level Domain spells will be 1st level spells, the 3rd level Domain spells will be 2nd level spells, and so on. What’s trickier is deciding on appropriate Channel Divinity effects, however, you can still refer to the existing features to determine what kinds of statistical benefits are appropriate.
The same goes for the other classes and their archetypes. Take a look at how the pre-existing features work, and see if there’s a way to accommodate what your player wants to do that works in a generally similar way.
–Pay attention to opportunity costs vs. statistical benefits. This is going to be your best method of telling if a proposed feature is potentially broken, and will also point the way to compromising with your player if she/he does propose something you suspect is broken. Not all that many class features are passive (that is, active at all times the PC is conscious), and when they are, they tend to pertain solely to skill proficiencies (such as the Bard’s and Rogue’s Expertise feature) or movement (such as the Barbarian’s Fast Movement feature). Therefore, any proposed feature that has statistical benefits in combat must be activated, either with an action, bonus action, or reaction.
The greater the statistical benefit being proposed, the greater the opportunity cost needs to be. Any increase in damage should require a bonus action at minimum, and if your player wants to increase her/his attack bonus, it’s fair to require spending an action to do so, with the attack bonus applying to her/his next attack. Any feature that allows an ally to do something outside of that ally’s turn must require that ally to use her/his reaction. Don’t allow anything that lets a player cast multiple spells of 1st level or higher on a single turn, and don’t allow anything that alters how a PC’s Spell Save DC or Spell Attack bonus is calculated. Any feature that increases the PC’s saving throw bonuses or confers any form of damage resistance must require a bonus action (at minimum) to activate, and last no longer than one minute.
–When in doubt, allow your player to use the build option on a trial basis. If you’re not sure if what your player wants to do is reasonable, and you’re not sure how to compromise with your player in modifying her/his proposal, you can always let her/him try it out on a trial basis, subject to your veto if you decide the created option is breaking the game. It’s best that you make this offer this as soon as possible, ideally during the same session (or correspondence) as you come up with the proposed build option. If your player gets used to using a homebrew option, she/he is going to get all mad if you take that option away from her/him out of the blue, and she/he will have a point, even if that option is broken.
–If your players broke the game, break it back! Perhaps you will create a PC build option that is totally ludicrous and game-breaking, and now that it has been introduced to the game, you are unable to take it away from your players. Now what? Well, introduce monsters and villainous NPCs that are doing the same stuff! Your game has already been made ridiculous, so keep going! Power gaming is always fun in small doses, and some of the most memorable gaming stories out there involve players and DMs allowing and doing things that are outrageous. Even if you don’t have that much fun in the short term, you’ll have a great story for your next group.