As far as I can see, there are no clear guidelines on what is involved in a character researching a new or modified spell. The downtime activities section of the DMG has crafting magic items and creating downtime activities but I'm wondering what would be involved in doing the following:
A player in my game is sick of losing barkskin all the time because of how easy it is to lose concentration. I think, fair enough - it would annoy me, too. So what about the character doing some research into making the barkskin spell a 1 minute duration (down from 1 hour) and no concentration? He likes that idea but I am not sure how to approach it.
A week and 50 gp? Chance of spell failure or unexpected consequence for the first few castings?
What would you do?
I award my characters with downtime and charge them time and loot for the goals they pursue. I treat the downtime like currency (so we don't RP it, just spend it). "In my downtime, I research a new spell."
Generally I charge 2 days per spell level of the spell in time and for cost I charge N^2 x 10 GP (where N is spell level). So a level 1 spell costs 2 days of downtime and 10GP. Level 2 is 4 days downtime and 40GP, level 3 is 6 days downtime and 90GP, etc.
If you run higher treasure levels, use units of 100 GP instead.
However, I'd be reluctant to mess with concentration much. It's like that for a reason. Are you sure you're setting the DCs right? It's not that hard to make that save.
El_Condoro wrote:
bawylie wrote:
Or he recognizes his limitations and develops a meditation skill, allowing him to use his proficiency bonus on Con Checks for concentration.
Or trains a feat. Etc.
Tempest_Stormwind wrote:
I would compare a new spell to a new magic weapon. For casters, the time, money, and eventual use would be similar I think for the process, so I would turn it into a downtime activity equivalent.
1. Look at the spell they want to make (barkskin with no concentration)
2. Decide if balances to spell keeps it at about the same level or change it to a stronger or weaker spell
3. Then look at the crafting magic items table for appropriate level and cost of such a thing.
a. if spell stays a level 2, then we can say the player must be at least level 3 to craft a new spell of this level
b. since the spell will be something new, we can bump it to the Uncommon level of rarity
4. rules for weapon creation require 25gp a day until creation cost is complete (500 gp in this case) and a spell slot of right level if required
5. you as the dm dictate if additional components are required and consumed during the process
So for a modified barkskin of about the same spell level, it would come out to about 20 days of intense downtime research and 500 gold in supplies/components/etc...as well as at least 20 casts of the original barkskin spell.
Onto the spell itself:
most spells that are longer than instant are concentration.
spells that are not concentration are generally weaker (mage armor)
new spell should not make the original obsolete
by making it not a concentration spell, it means it can now be stacked with other concentration spells
advice:
rather than the current plan, let them create a druid version of mage armor. It's weaker defensively, but lasts much longer without concentration. It's balanced since it's already written. It will be cheaper and faster to produce with downtime.
Novama wrote:
I like what you came up with. Some of the values seem a bit arbitrary to me, but overall, it's a very elaborate and creative process.
I wonder if you misread barkskin. Barkskin just gives you a limit on how low your ac can be (16). You don't add dex to barkskin or additional armor. You calculate ac as normal. If the amount calculated is less than 16, your ac becomes 16 with barkskin. If your ac is 16 or greater, you experience no changes to ac.
Mage armor works as you stated. No armor allowed and it becomes 13 + dex mod. Comparatively, the spells are very similar in the boost they give to ac.
What you wrote makes me think your druid (non shapeshifted) would have a 19 ac the way you calculated it. I can see how you would think mage armors details are no comparison if that was your interprentation of the spell.
He has a +0 Dex mod in either form, so mage armor would give him AC 13 (he can't wear any armor for the spell to work) whereas barkskin gives a flat AC 16, as you said. So the brown bear's natural AC 12 would only be improved by 1 for him and not worth the loss of a spell slot (his or someone else's) - arguably.
The values in the document are absolutely arbitrary. 
There's no doubt that a barkskin spell would be more advantageous in the situation, but since the druid can already weild equipment that would make barkskin unnecessary, I would see this as purely a means of buffing his wild shape.
I would then consider the balance of the request with that in mind.
The rules you posted seem to cover what you need already and a quest for this specific spell seems appropriate due to its obvious intended use. After looking at the cr from the boosted ac, I have decided that the power difference is negligable. A happy player and a happy dm. Must be a win win