This rough preliminary design (Adam volume 54/1/50) for the semi-dome of the apses shows the plasterwork ornamentation very near to the executed scheme which makes use of a peltoid shield in the central compartment.

The wall elevation shown in Adam volume 1/159 was executed with alterations. The executed chimneypiece is not shown here, the figurative panels shown above the niches contain alternative scenes, and the whole room has an arabesque frieze instead of the anthemia frieze shown in the drawings. Moreover, there are no masks in the executed fluted string course. Adam volumes 1/160-161 show the apsidal ends of the room almost as executed, again without their arabesque frieze, and with a slightly alternative ornamental scheme in the demi-domes. This was the first room at Syon to be completed by Adam in 1763.

Various features of this room were clearly inspired by what Adam had seen in Rome, most notably the sculpture and grisaille panels, but according to Stillman there are also elements derived from Adam's training in Scotland, including the modillioned cornice, the rinceaux frieze, and the large overmantel. The grisaille panels were executed by Andrea Casali at a cost of £200.