You can plot pdf's onto any sheet size you may need to change your pdf printer to allow you to choose more sheets alternatively pick properties and it may allow you to creat a custom size.
I would expect that 36x24 pdf's will become huge why not create at 1/4 scale you shouldn't lose any clarity.
Also I, like I am sure others here have gone round in circles trying to make pdf's plot at a scale of 1:1 when checked with a ruler. Direct Plots are perfect. Spent a lot of time getting tiffs to reproduce at 1:1 also.