There is a couple of research papers on bin packing with variable bin sizes, e.g. [1, 2]. You can probably find most of them with scholar.google.com, and you might get some more results if you look for "(2d) cutting stock (with) variable stock (sizes)" or for the "(two-dimensional) assortment problem".
In most papers it is assumed that you have a finite set of bins with different, but fixed dimensions to select from (as opposed to your problem, where both dimensions seem to be free). A notable exception is [3] (maybe there are more, but it's the only one I have come across).
There is also quite a lot of literature on the strip packing/cutting problem, which deals with the case of one fixed and one "infinite" dimension.