I will be pouring concrete for a patio, concrete will be next to house foundation, the house has a metal around the outside wall, what measurement should I have new concrete not to obstruct the function of the metal piece in the outside wall?

Do you mean metal flashing? That keeps water from backing up under the siding. Depending on how protected the patio will be or not, keep it about 3 inches below the bottom of the flashing, and seal down the flashing with something tarlike if you live where snow will accumulate against the house.
If a door opens onto the patio, often the patio will be one step down, about 7 inches. You don't want water seeping in the bottom of the door either.