create table if does not exists

I try to have the following stored procedure, to help me create tables, if the table does not exists (Is this a good practice by the way?)

if not exists(select * from information_schema.tables where table_name = 'MYTABLE') then

RAISE NOTICE 'table not there yet.';

CREATE TABLE MYTABLE
(
"value" text NOT NULL
);

end if;

When I run for the 2nd time, 'table not there yet.' still being printed out, al though I check through pgadmin, the MYTABLE is there.

May I know how I can fix this?

Thanks and Regards
Yan Cheng CHEOK