Note on the optional additional stage
The official GR92 circles the retort town of Empuriabrava and leads from Roses through the flat, agriculturally used hinterland. This is also worth seeing, but it would take a whole day to go around Empuriabrava. And in the evening you would be in no-man's land with no place to stay.
We therefore recommend skipping this part of the official GR92 and instead taking a taxi from Roses to Empuriabrava and joining stage 4 there. Since the last part of stage 3 leads mainly through urban areas and past the harbour, you should even consider calling a taxi at Platja Almadrava (e.g. at www.costabravataxi.de, owner speaks German).
For those who absolutely want to walk the "real" GR92, we have drawn the map for the additional stage here: Map for the additional stage. Overnight accommodation is only available at the stage destination during the high season with your own tent at the Almata campsite, or you can branch off to Empuriabrava in good time (Link: Camping Almata). We therefore recommend skipping the additional stage!