- Have the player mage describe the spell they want to make in a single sentence.
- Each word in the description is a word you can put into an auto-crossword creator like this one: https://www.puzzle-maker.com/CW/
- Each box of the crossword is a book they need to find or buy that loosely corresponds to the subject of that word.
- Boxes at the intersections of the words are harder to find and are about both topics.
- Each book should be 1d6 100gp
|Dart Seeks Enemy Mage example
The intersections of the words on the crossword, like the first square of 2 Down, are something more difficult to find. In this example Enemy crosses Seeking. So, maybe the book here would deal with even determining that someone is a threat-- Divination of Hidden Enemies-- or maybe it would be Esoteric Auras of those Using Magic. I would say if we can buy one of these rarer books it should be more expensive 1000-6000gp, but more likely it would be worthy of a mini-quest.
More words or more complicated words make for a bigger library requirement and more expense. I think part of the fun of it would be the player putting the spell they want into as few words as possible. And I don't think the DM needs to be the devil in negotiating here, trying to trip them up. The point is to produce fun.
Some other thoughts. The books the player acquires could be used to research other spells later. This would make it feel like they actually had a research library, if they could say something like "I have a good selection on magical Seeking." One potential problem is that players don't know what spells they might make, especially newer players. For my game I thought about making a new spell a requirement for joining the City Mage Guild, to kind of force the issue. If the player has a hard time coming up with a specific spell idea, I can have the Guildmaster suggest something they need.
A bigger problem could be that the potentially powerful effects that are traditionally kept from players by higher spell level would be easily available here. I mean like damage causing spells that always hit or spells that incapacitate enemies. With this simple word system there is nothing to keep a player from making a super powerful spell. I guess that might be the DMs role, to negotiate this, and say for example "Traditionally in this world, it has been very difficult to put more than a few weak minded fools asleep at once," etc.
But, anyway, I think it might be fun, let me know any ideas you have.