Your portal must be created in a direct line with the walkway (the bit with the copper blocks), so that people are able to walk from one portal to the next. Your portal must be 2 blocks wide by 4 blocks tall. 8 Portal Conduits will be provided for this.
If you want to build a different sized portal, you can do so, but you must speak with the player your portal will connect to and confirm that you will both use the same size (details of where your portal connects to should be on the plot notice).
Sorry to hear about your base disappearing too - need to keep those beacons fueled!