[Konstantinos]

You need the z (height) and that can be found by GetVehiclePos function. I added + 1 to the current height just to prevent it to be underground. If it's over the ground though, you can remove it.

pawn Код:

GetXYZInFrontOfVehicle(vehicleid, &Float:x, &Float:y, &Float:z, Float:distance)
{
    new Float:a;
    GetVehiclePos(playerid, x, y, z);
    GetVehicleZAngle(playerid, a);
    x += (distance * floatsin(-a, degrees));
    y += (distance * floatcos(-a, degrees));
    z += 1.0;
}

You don't need the rotations of the vehicle.