http://www.dandwiki.com/wiki/SRD:Developing_Epic_Spells
Or even, would a spellcaster be allowed to research existing PnP epic spells with DM supervision, to use in specific events? Like, for instance, Rain of Fire. It would be awesome fun for say, an epic evil spellcaster to research this spell, and use it to deforest an area to tick off enemy druids.
Rain Of Fire
Evocation [Fire]
Spellcraft DC: 50
Components: V, S
Casting Time: 1 minute
Range: 0 ft.
Area: 2-mile-radius emanation
Duration: 20 hours
Saving Throw: Reflex negates (see text)
Spell Resistance: Yes
To Develop: 450,000 gp; 9 days; 18,000 XP. Seeds: energy (fire) (DC 19), energy (weather) (DC 19). Factor: change rain to wisps of flame (ad hoc +12 DC).
This spell summons a swirling thunderstorm that rains fire rather than raindrops down on the character and everything within a two-mile radius of him or her. Everything caught unprotected or unsheltered in the flaming deluge takes 1 point of fire damage each round. A successful Reflex save results in no damage, but the save must be repeated each round. Unless the ground is exceedingly damp, all vegetation is eventually blackened and destroyed, leaving behind a barren wasteland similar to the aftermath of a grass or forest fire. The fiery storm is stationary and persists even if the caster leaves.