I've used ceiling tiles also. While they work well, I find that T-pin don't always have enough holding power and tend to loosen after a while. Plus the surfaces on they are rather fragile and tend to flake off easily, the dust from which is glass fibre and I don't like to breathe if I have a choice. Plus (or is it a minus), you can't exert too much force on it, or it'll dent.

Still, I've built many a plane straight and true with ceiling tiles - the fibrous cement kind - not the bonded fibreglass kind.

If you have room and can afford to build a stout work table, I find that a piece of sheetrock makes the ideal work surface. It is hard, heavy and flat, so corners don't lift like other lighter material. The paper surface and gypsum below hold T-pins extremely tight. You can even write notes directly on it. Best of all - it cheap!

My current workbench has a piece of sheetrock about 4'x8' and is indispensable for embarking on giant scale projects.

BTW, if you get a slab door for worktable, be sure to get the solid core, not hollow core, which will droop in time if you got any sort of load on it.