Target one object weighing 10 pounds or less that you can see within 30 feet. Gravity's pull is altered by 180 degrees for that object for the duration, causing it to "fall" upward, accelerating at a rate of 10 feet per second per second to a maximum altitude of 200 feet, where the object hovers until the spell ends. When the spell ends, gravity effects the object normally, and it falls in the next round. Any creature or object struck by the object (falling in either direction) takes 1d4 bludgeoning damage for every 10 feet of fall to a maximum of 20d4. Creatures in the object's path that can see the object and are not immobilized may make a DC 10 DEX save to avoid being struck. (At the DM's discretion, the object takes damage up to 20d4 upon impact. For example, a 10-pound stone falling into a deep pool or water would take no damage, but the same stone falling onto a pile of similar stones may shatter into hundreds of pieces; the same stone striking a creature would likely take half the damage dealt to the creature. If the object is instead a glass bottle or wooden bucket, it will likely suffer as much or more damage than it deals.)
If the object strikes a creature, the creature must succeed on a DC 9 DEX saving throw or be knocked prone.
If the rising object collides with a solid object, such as a ceiling, it rests there for the duration and then falls normally in the next round.
This spell cannot target a creature regardless of weight.
In the sentence "Any creature or object struck by the object (falling in either direction) takes 1d4 bludgeoning damage for every 10 feet of fall to a maximum of 20d4." instead of "10 feet of fall", consider "10 feet the object has fallen."
I think the save to avoid being knocked prone should be a Strength saving throw and be DC of 10.
Make the parenthesized note and make it into it's own paragraph after the following two. The first three paragraphs should be combined into one. And the note at the end is unnessary as you began the spell by outlining that only objects could be effected.