What makes the ruin at Rossaneny quietly arresting is how precisely its collapse can be read: the south wall still stands at nearly three metres in places, while the east and west gables have been reduced to little more than a metre, and the north wall survives somewhere between the two. The building does not present a romantic silhouette so much as a record of differential decay, each wall failing at its own pace.

The church is a rectangular structure, measuring 15.2 metres in length and 6.6 metres across internally, with a layout that makes no architectural distinction between nave and chancel, the two zones that in more elaborate medieval churches would be separated by a chancel arch or a change in floor level. This undifferentiated plan is typical of smaller, rural Irish parish churches, built to serve modest communities without the resources or liturgical complexity that would demand a more elaborate arrangement. In the south wall, a doorway sits four metres from the west end, and the remains of a window survive closer to the east end, though only the eastern jamb is still standing. Among the several piles of collapsed masonry scattered across the interior, one piece stands out: a sandstone block bearing a chamfered window sill, a detail in which the edge of the stone has been cut at an angle to allow rainwater to run clear. It is a small refinement, but it suggests that whoever built this church paid some attention to finish and craft, even at this modest scale. The church occupies the south-east angle of the surrounding graveyard, which continues in use as a burial ground.