I've been contemplating setting up a chart or something for allowing warforged to pick up some additional stuff for an ECL. For some reason, I have a recurring image of a warforged with wheels, and thus a faster move speed, running around in my head. A warforged designed as a scout/fast recon unit seems like it might be amusing, if you pick up some of the archery feats and Shot on the Run.
For large size, it's not terribly clear. Just being large, without any further modifications, I'd just peg as a solid +1 ECL. It's good, but not really overpowered IMO. This is a fairly debatable point, but that's how I feel about it. Most of the time, you get a few points of Str and Con for increasing to Large size, and lose some Dex. This usually pushes things into the ECL +2 category.
In Eberron, the warforged are set up so that you buy additional modifications with feats, not ECL. Being Large is too good to be set up like, say, Body of Adamantine is. You could, I suppose, say that it takes up your 1st level AND your 3rd level feat slot, but that's a bit kludgy design, IMO.
If somebody in my group wanted to do this, I'd give them +4 Str, an additional +2 Con, and -2 Dex in addition to the warforged base stat modifiers, and maybe a slight increase in the base warforged armor. I'd just call it a straight +2 ECL at that point, meaning that you couldn't play it before 3rd level, when you'd have one class level.