In “Elves of Evermeet”, how does the “construction” spell work?


This is in the 2nd edition book: Elves of Evermeet. On page 65 there is the description for a spell: Construction. Part of the description says:

The caster can create any object with a volume equal to 1,000 cubic feet (10x10x10 feet) per level. Each 1,000 cubic feet so created takes one entire day. Once created, the object can be added to at the same rate (1,000 cubic feet per day) for as long as the caster wishes.

This made me wonder, assuming a level 20 caster, how much volume can be created/added to in a day? Is it 1000 cubic feet/level, or only 1000, in which case, what is the point of mentioning the caster level?