how to create a new composite type using already existing composite types

Hi,

Is there a way to create a new composite type using already existing composite type?

For example,

CREATE TABLE inventory_item (
name text,
supplier_id integer REFERENCES suppliers,
price numeric CHECK (price > 0)
);

produces the following type automatically
CREATE TYPE inventory_item AS (
name text,
supplier_id integer,
price numeric
);

but I'd also like to have a type with an extra column for certain functions

CREATE TYPE inventory_item2 AS (
name text,
supplier_id integer,
price numeric,
size integer
);

but it would be handy if I could reuse inventory_item instead of having to retype the whole lot. I can't work out or find the right syntax, can anyone show me how? Any help would be much appreciated.

Regards
Iain