Chambers never visited Ireland and so he was nor able to supervise the construction of his design. Charlemont engaged Simon Vierpyl whom he had met in Italy to supervise the construction of the Casino. Vierpyl's knowledge of stonework and building techniques enabled him to pass on this knowledge to his Irish workers. He was responsible for the superb detailing of the Portland stonework, so much part of the character of the Casino. Chambers himself acknowledged Vierpyl's skill when he wrore of the Casino that it " was built by Mr Vierpyl with great neatness and taste." Some think that the stateroom may have been designed by Vierpyl .
From a distance the Casino looks like a cube of Portland stone. It is built in the plan of a Greek Cross. Each corner of the cross is framed by pairs of columns. There are four more columns at each of the four corners. The columns also are hollow in the centre and were used as down pipes for taking the water from the roof. The water trickled down iron chains inside the columns and it made a lovely singing sound when there was very heavy rain. On top of these columns and running right around the building is a carved frieze of ox skulls and shields. As you approach the Casino you can see two urns carved by Cipriani on the top. These are a very cleaver design for chimney pots. At each of the corners there are reclining lions with a lovely font under them. Originally Charlemont had intended that these lions would have a fountain from their mouths (that is why they have a smile on their faces) and that the water would drain away through the ornamental carved fonts. But because the fountain never materialised the fonts became panels which were carved by the famous sculptor Cipriani. There are four sculptured gods over the front and back of the Casino. These are Bacchus the god of wine; Apollo the god of purity and the sun, patron of musicians and poets; Ceres goddess of grain, harvest and agriculture; and Venus the goddess of love.
The main entrance is quite spectacular. The main door is of unpainted oak which when weathered took on the same colour as the Portland stone of the building. You enter the building through a two-leafed door which only rises half way up the outside door. These two doors could be left open and Chambers designed a window to drop down and allow the morning sun in the hall. When you look at the windows you notice that the glass reflects the light and that you cannot really see in. Chambers used curved glass which reflected the light in the window panes. The reason for this is that some of the windows are dummy windows just there for to achieve the exterior classical balance.