Room sizes vary from centre to centre, to see the exact specifications of accommodation at each resort click on the 'accommodation' tab in the relevant resort page. The rooming is handled by UCPA staff in the centre and is planned a few days before arrival.
If you are travelling with friends you should book together as as part of a group (when you login to your booking you can see your group members). UCPA always tries to room groups travelling together in the same room. It is unlikely but in some circumstance this isn't possible friends may be roomed separately. If your group doesn't entirely fill a room you will be sharing with other people. The only way to guarantee you are roomed with a friend is to book a private twin room.
If you are a solo traveller UCPA will do what they can to room you in a single sex shared room. UCPA makes every effort to try and match solo travellers with those with the same native language and/or of similar ages. Solo travellers can't select the twin room option as this is for two people travelling together only.