I'm not sure if this is deliberate or its elsewhere and I've not seen it, but the Flood Gate doesn't appear to have a crafting recipe defined in BuildCraftFactory.java loadRecipes().

Perhaps iron bars, a golden waterproof pipe, and as it can be switched on and off, a piston (I just guess the name of Iron Bars...)
e.g.

if (floodGateId != null)
CoreProxy.proxy.addCraftingRecipe(
new ItemStack(floodGateBlock),
"bpb",
"b b",
"bPb",
'p', BuildCraftTransport.pipeFluidsGold,
'b', Item.ironBars,
'P', Item.piston);

Or perhaps to match the texture better, iron ingots in the four corners?

Derp, I always forget the recipes. Damn.

Hehe. That makes me feel good that I got to contribute something the great CovertJaguar missed. :-)
I've no idea how to submit PR's so will leave you to do it. :-)