I recently whipped up a 5e play-test for the Permanency spell from 3.5e, and my four players enjoyed it in the 3 mid-level (Lvl 9-14) adventures we played with it.

I created it out of a desire for more resounding spell effects. As it stands, there are a lot of spells in 5e that wear off quickly, or require copious amounts of casting for them to remain permanent (I'm looking at you, Teleportation Circle, Hallow, and Private Sanctum and your 360 day casts to become permanent).

For Version 0.2, I am already am re-writing most of the spell.

Additionally, I wish to  make it sound more as if it belongs in an official publication and thank everyone for their suggestions and criticism.

Beta Changelog:

1. Added Spell Template borrowed from 3.5E SRD, and reworked to work with gold in place of EXP.

• Not Published.

Beta Issues:

• Players frivolously using the spell when it was simply a gold-based cost, after 13-16th level. And transmuted wealth was being used for components.

Changelog for V0.1:

1. Added Additional Spells valid for use with Permanency.
2. Change Use EXP cost instead of Gold. (V0.2)
3. Change Casting time reduced to 1 reaction, to allow subtle casting of Friends/Hex on NPCs. (V0.2) 

• Published.

V0.1 Issues:

• Complications with Experience costs. (V0.2)
• Complaints of making Casters even more gamebreakinig than they already are.
• Under-leveled Casters. (V0.2)
• Too low Spell Level. (V0.2)

Changelog for V0.2 (in progress):

1. Change Casting time to 2 hours, from 1 Reaction. Added note that Concentration requirements are now removed.
2. Change The Spell is now 7th Level, from no longer 5th (also Removed from Warlock spell list)
3. Change Gold cost system is now in effect, replacing the EXP system, with further edits to accommodate for spells that edit base stats (e.g. Size, Speed, Magic Detection).
4. Change Edited all header sizes, and made Spell Headers larger than the DMs notes and Gold cost chart.
5. Added Gain 4 Levels of Exhaustion upon casting the spell, which also reduces Spell DC by 2 per level of exhaustion. These cannot be magically reduced.
6. Added Enhance Ability has its temporary HP refreshed after a long rest.
7. Added Rope Trick as an available spell.
8. Removed Magic Weapon, to include a note that +3 weapons cannot be made.
9. Removed Friends, Hex and Animate Objects, due to not fitting my desired function of the spell (Augmentation and Utility should be the focus, not combat).
10. Rewrote the recommendations at the bottom to be more straightforward, and updated notes on optional 7th Level spell Magical Mansion.

• Published.

Issues for V0.2:

1. Pending Comments...

Permanency spell link(s) here: [Link V0.1[ [Link V0.2]

Thanks all!

The link doesn't seem to take me anywhere. So I can only share my initial thoughts: Permanency was deliberately left out of 5th edition as a result of a dramatic change to the number of spells which a single spellcaster can load-up on someone and put severe strain on both the party-to-enemy balance and PC-to-PC-contribution balance of the game. Basically, not having a permanency spell is one piece of the puzzle to preventing what was referred to as "linear fighter, quadratic wizard" unbalace of the game where-in some classes get incrementally more powerful at higher levels, but those with access to spellcasting grow much more powerful over the same game-play time.

As-is, 5th edition characters are fairly close in their ability to make meaningful contributions toward their party's success at any level of play - putting a permanency spell back in the mix makes any classes that can access it just plain better than any other classes once they have it, no matter whether the cost is GP for expensive consumed components or XP (which is separately is own bad idea because the end result of things having an XP cost is that the character is both lower-level and more powerful, which further skews the above-mentioned balance of the game in both the vs. enemy and relative to other characters areas of balance).

So my advice is to leave turning a spell into a permanent effect as something that a character can cast wish to do, following the details of the last two paragraph's of that spell to the letter.

I understand where your coming from, and aim only to make some DM's games have more lasting effects of wizards magic (such as building, utility, and augmentation of characters).

This spell is aimed more at making the world into an evolving place, with casters magics having a lasting effect on what is around them.

I was also considering allowing players to share the EXP cost for the spell, which would assist in both casting, and preventing under-leveled casters.

As a side note, I realized because of your post, that I posted the creator-specific URL instead of the public access one. I totally overlooked that.

Permanent hex?  I am horrified by that and almost everything else about this spell.  Put some more limits on the spells it's compatible with!  Please. 

Permanent Hex was added with much hesitation on my part; Though I did point out earlier in the spell and it's rules, that you can only have each spell cast once on a particular target.

Thus preventing infinite d6s for damage, or giving an all skills checks disadvantage. I hope this makes sense as a limiter.

Though I should likely clarify that having a Permanency-effected Spell cast on you also makes you immune to another casting of lasting buff/debuff spells such as Enhance Ability, or Hex.

Is this the problem you were meaning, or, if not, could you clarify about what you see as the issue for Hex?

• I think, at the minimum, the action economy is off - to permanentize something as a reaction is a bit horrific.
• Given its game impact (in a system that now uses concentration) the level should be increased - likely to 7th.
• The exp cost is a bit 'hinky' - ie overly complicated by comparison to the 5e rules RAI, If you were going to simplify such - I'd consider that back to 1st/2nd ed. where the spell cost a point of constitution permanently - or at least until dispelled. 
  
  When you are getting into that level of exceptions/caveats you're already dealing with the fall out from the mapped attempts to make that work with the rule set, your exceptions and caveats exceed the text of the spell, that is an indication of a design issue right there, so I'd suggest finding a simple solution to the complex problems you've created in this spell. 

 SO,
Increase the level ;
Increase the casting time - like a day would be nice, but at the VERY least 10 minutes of concentration - either during which the spell is maintained (Meh) or after which the spell to be made permanent is cast as part of the casting. (like an attack with a weapon is part of various other spells)

and, Add a more simplified cost;
      like 1 Con (doesn't return until the permanency is dispelled even on Greater Restoration)
      or x thousands of GP per casting 

Yes, this could mean a +1 weapon is created in day - but if is a 6th or 7th level spell slot that costs you CON and 5,000-50,000 gp... you're not going to do that except for emergencies - more so if a dispel magic would unravel the spell.

I'm currently changing mechanics around to see what works/makes sense for casting purposes, and I'm leaning towards a longer ritual casting with a special tag.

I also hadn't toyed with bumping it up as of yet, but I will concede that 7th-8th level makes more sense considering all the spells uses/benefits.

And as of my last mock-up of the spell in a playtest, I believe that I'll be changing it to a gold based cost that'll likely be 2-5 times more gp than the current EXP cost.

And back to casting time; a 1-2 hour ritual casting time that gives 3-4 levels of exhaustion sounds like a pretty effective way to cut down abuse, as even the bravest caster would be unlikely to brave such a penalty repeatedly in a week's span. With perhaps a leaflet from Wish's book, with a -2 casting DC penalty per level of exhaustion until said exhaustion is brought back to 0.

Though; It should be noted that the reaction casting time was thought up to simplify casting a spell such as Friends, or Hex on an NPC to effect skill checks involving them.

I'll likely just remove those two, and Animate Object, as they don't fit the theme of augmentation and utility.

Edit: 1-2 hour ritual, not 3-4 hour. And more specific DC detriment.