How to declare an array of objects in C#

The issue here is that you’ve initialized your array, but not its elements; they are all null. So if you try to reference houses[0], it will be null.

Here’s a great little helper method you could write for yourself:

T[] InitializeArray<T>(int length) where T : new()
{
    T[] array = new T[length];
    for (int i = 0; i < length; ++i)
    {
        array[i] = new T();
    }

    return array;
}

Then you could initialize your houses array as:

GameObject[] houses = InitializeArray<GameObject>(200);