Simple script to find files and give file size sum

Hello all,
I'm kinda stuck on a very simple task.
I have this small piece of code to find files and report the file size.
In the end, Im going to use it to search specific folders, exclude certain file extensions and report.

But I'm drawing a blank on how to give the total sum of the FileGetSize while running it through.
Please help :-)

#include <Array.au3>
#include "RecFileListToArray.au3"
$aList = _RecFileListToArray(@UserProfileDir&"\documents", "*.*", 1, 1, 0, 2)
For $i = 1 To $aList[0]
Local $iFile = $aList[$i]
MsgBox(4096, $iFile, $iFile)
$iSize = FileGetSize($aList[$i])
MsgBox(4096, $iSize, $iSize)
Next