Caesar's a great source for stuff like this. Near the beginning of book 2 of the Civil war, there's a detailed description of a novel type of tower and moveable shelter that some of his soldiers devised at Massilia. Here, Caesar uses the adjectives longus and latus, and then puts the measurement in the accusative (an accusative of extent of space, I suppose):
storias autem ex funibus ancoriariis tres in longitudinem parietum turris latas IIII pedes fecerunt… [BC 2.9.5]
'mats 4 feet wide'/'four-foot-wide mats' (lit., 'mats wide to an extent of 4 feet')
ubi ex ea turri quae circum essent opera tueri se posse sunt confisi musculum pedes LX longum ex materia bipedali quem a turri latericia ad hostium turrim murumque perducerent facere instituerant. [BC 2.10.1]
'a shelter 60 feet long'/a 60-foot-long shelter' (lit., 'a shelter long to an extent of 60 feet')
Therefore, you can say something like cubiculum metra II latum ac (metra) IV longum est, or the office can be described as metra II latum ac IV longum.
This isn't quite as pithy as '2 by 4 meters,' but it's somewhat lighter than cubiculum latitudinem duorum et longitudinem quattuor metrorum habet.
If the length and width of the office are equal, you can adapt this bit from earlier in the same passage:
patebat haec quoquo versus pedes XXX, sed parietum crassitudo pedes V. [BC 2.8.2]
'It extends 30 feet on each side'
(Note: quoquo versus can also be written as a single word, and versum and vorsum are sometimes found instead of versus.)
Therefore, for an office that is 8 meters square (as opposed to 8 square meters), you can say cubiculum patet quoquoversum metra VIII, or the office can be described as metra VIII quoquoversum.