Rebecca Flynn was the first and only choice for Laura. She had previously been cast only in Girl Next Door roles in serious dramas. The character was written specifically for her to play someone closer to her own personality. As the writing process went on, some of the scripts literally had the stage direction "Rebecca will make it funny".
Lindsay's characterization in the pilot episode was initially that of a dumb blonde who was picked on by the other girls in the house. Much of her resulting persona was influenced by the casting of Ellen Jones - especially her being a drama student. One episode has Lindsay ranting about her part in a play being cut down to three lines - which comes from something that happened to Ellen herself.
Ingrid Igoe brought the black and silver bra to be used as a prop in an episode that was scrapped called 'Busted' (where Sadia attempts to prank Roisin by putting her bra in the fridge). She brought it to set a couple more times, and it became featured in more episodes. For example in 'Miss Lucy', Lindsay was scripted to just throw a bag at Roisin; it was changed to accommodate the bra.
The 'Party Animals' episode was originally written as a separate sketch, involving two male housemates that opened with the aftermath of the party and the landlord as an off-screen character. It was incorporated into this.
Bobby Calloway briefly considered playing Robbie himself but wanted to focus on directing. He did however play the smaller role of Marty just to be able to say the "nay I say" line.