I took a look at the AIM for FAA basic PPL licence to see what it says on VFR minimums. From the extract below VFR flight above a cloud deck is legal so long as you are 1000 feet above the cloud deck.
"VFR on top" as a clearance is actually an IFR clearance (i.e. your IFR flight plan remains active but you have more flexibility to select your altitude - a bit like a "Contact Approach" which is an IFR approach (ATC seperation) but in visual conditions not flying the published procedure.
FROM THE AIM - Basic VFR Weather Minimums Airspace Flight Visibility Distance from Clouds
Class C
3 statute miles
500 feet below
1,000 feet above
2,000 feet horizontal
Class D
3 statute miles
500 feet below
1,000 feet above
2,000 feet horizontal
Class E
Less than 10,000 feet MSL
3 statute miles
500 feet below
1,000 feet above
2,000 feet horizontal