It's very difficult to predict. If your siding were an infinite, perfectly conducting plane, then the results would be the same as if you had another inverted V, positioned as if mirrored through the plane of the siding, but fed in antiphase. This is called an image antenna.
What this does depends on the distance between your antenna and the siding. It's not unlike the problem of a dipole over ground.
Here's the rub: your siding isn't infinite, and it isn't perfectly conductive. The geometry is going to significantly change the result. You might get some result by putting the measurements precisely into a modeling system like EZNEC, but short of that it's hard to say.
An inverted V isn't a very directional antenna to begin, so it's not too productive worrying about how it's going to affect the pattern. It will probably significantly affect the tuning of your antenna. And, this siding is going to have some significant RF currents in it. If it's lossy, because it's not conductive, it's also going to degrade the efficiency of your antenna.
But, if this is the only good place you have to put an antenna, it will work. I doubt the losses will be too huge, if you can get it to tune. That's probably the hard part. Will it tune? Again, really hard to say. Wire antennas are cheap. The easiest thing to do is try it and see.