Once you've finished painting the wall, you may go home right away.
Literal
Wall [object-を] paint-finish-[if-たら], immediately go-home-even fine [assertion-よ].
塗り終える is a compound verb: 塗る (paint) + 終える (finish) = 'finish painting.' The ~たら conditional sets the timing: 'once you've finished.' 帰宅してもいいよ gives permission with the casual よ. The sentence structure is conditional + permission.