Elongating cells in a Westok beam costs absolutely nothing. Westok do this free of charge for the project fabricator.

In a recent project Hove City Park, the cell arrangement was alternate circles and elongations, with 5 elongated openings in every beam.

Best practice is to place elongations away from supports, where no stiffening will be necessary. However, elongated openings near supports are perfectly possible, though it may require stiffening, normally carried out by the project fabricator.

CELLBEAM Auto Mate designs elongated openings, and the stiffening should it be necessary for such openings near supports.