Is there any accurate information on how high the-wall is?
From the ASOIAF wiki:
The Wall is a massive barrier of mostly ice stretching across the northern border of the Seven Kingdoms, separating it from the wild lands beyond. The Wall is one hundred leagues long (three hundred miles) and reaches over seven hundred feet at his highest point, although some foundation blocks in hilly regions, such as near Greyguard, send it nine hundred feet in the air.
Measurements in the Seven Kingdoms in both the books and TV series are given in imperial measurements. The Wall is about 100 leagues or 300 miles (482 kilometers) long, about 700 feet tall (213 meters) and averages 300 feet in width (91 meters).
In case you were looking for an answer directly from the literature, I happened to find a relevant passage while reading today.
On page 154 of A Game of Thrones, it says,
...but it was only the north that concerned the Night's Watch, and to the north loomed the Wall. Almost seven hundred feet high it stood, three times the height of the tallest tower in the stronghold it sheltered. His uncle said the top was wide enough for a dozen armored knights to ride abreast. The gaunt outlines of huge catapults and monstrous wooden cranes stood sentry up there, like the skeletons of great birds, and among them walked men in black as small as ants.