Sounds like a lot of work...I used straw bales for the north wall of my greenhouse and they have lasted for three seasons...I just built the whole thing on top of them....This year i am going to use the old straw for mulch and then put in new ones...

Not much insulation value in the manure or sawdust.... Especially if they get wet...

Happy building
~SeedPlanter

some old friends of mine came up with the idea of using their giant compost pile with kind of roman heating system to warm up their greenhouse through the floor. it was pretty cool

That's right. Generally the manure is applied as a heap, or even under the floor-boards (most greenhouses don't come with floor-boards anymore), but you'd get a similar effect from a manure wall. I'd suggest having a second kind of insulation on the outside of the wall to direct the majority of the heat inwards, but the mass of the maure itself will help some. Also, you'll more years out of the wall if you line it with polyethylene plastic or EPDM pond liner (less rot from manure-wood contact). Still, for shear ease and economy you're better off just filling the wall-space with dirt--you get it for free if you can use on-site dirt and you won't have to mess with adding and then removing the material as much as with manure (actually, never in the lifetime of the wall).