Cover giblets, celery, onion and pepper with water in a 3-qt saucepan.
Bring to a boil, reduce heat and simmer for 20 minutes.
Remove giblets and neck, set aside to cool.
After removing turkey from roasting pan, discard all the fat from the pan.
Add stock and bring to a boil, scraping the bottom of the pan.
Add diced giblets and the meat from the neck
To make a roux: in a separate pan, melt the butter and add the flour. Cook over medium heat, stirring constantly for 5 minutes.
Add enough of the roux to the boiling liquid to achieve desired thickness.
Simmer for 5 more minutes and season with salt and pepper.