I work as a paint shop prepper at an airport in the UK and have currently worked on a aileron of a 757-200 that was 14ft long and wanted to compare it to that of a A380
A good source of public information is the aircraft characteristics document that the manufacturers typically publish for each model, including the A380.
A scale planform drawing can be found on page 310 of the PDF, subject 8-0-0. Based on this drawing, the rough size of the ailerons can be estimated.
The aileron is divided into three sections which move independently (see Why do some aircraft have multiple ailerons per wing?). The outboard section is about 4m (13 ft) long, the middle section is about 3m (10 ft) long, and the inboard section is about 2m (6.5 ft) long. In total they are about 9m (29.5 ft) long.
Derived from Airbus document:
Ailerons viewed from cabin: