I think its great that the game offers both the option to use the mouse as well as the R & T keys to rotate buildings during construction. I think it would be a relatively simple yet great addition for buildings that were rotated using the R & T keys during construction, to retain their orientation while being built repetitively.
An example: I like to adjust the orientation of Holding Areas using R & T keys by aligning them to the environment. If I then choose to construct another Holding Area it will snap back to its initial alignment, requiring me to once more align the building using the R & T keys. It would be amazing if the first time I aligned the building could carry over, thus greatly speeding up construction.