We know that the rents in Freiburg are very high, compared to other parts of Germany. But to help you to find a suitable room for your stay in Freiburg, check the following:
-Studierendenwerk (dormitories) www.swfr.de
-Studierendenwerk (private rooms) www.swfr.de/en/residence
-shared flats: www.wg-gesucht.de
-single apartments: www.immobilienscout24.de
Additionally, it's always good to check out the larger facebook groups about Housing in Freiburg!