Abominations are large, fleshy giants. Not giants in the literal sense, but just very large. Perhaps two to three men tall, but making an average measurement of them is pointless, because they are constructs, and can be built up however the creator chooses. Abominations are commonly quite fat, and often have multiple extra organs to improve performance on the field.
Abominations are made from the strewn together parts of bodies. They are covered in stitches and mismatched flesh. Abominations do not look anything like humans. Their legs are more like that of an elephant’s, and they have multiple arms attached to a bulbous, sweaty, bleeding, gory body. They could be sentient, but this is entirely up to their creator of how much brain power the undead has.