Any wizard of any level can attempt to invent new spells. The only absolute
requirement is that she be one level higher than the minimum level to cast spells
of that level. Thus a 1st-level wizard can only invent cantrips. The basic roll
is on d% against the total of the wizards level and her Intelligence, minus 5
times the spellšs level. Add the level of the highest-level similar spell the
wizard knows. For every week spent in experimentation, divided by the level of
the spell, add 5%. Research can also aid, though the exact adjustment depends on
what is found.