Hi i have to make a 12" square cake and was wondering what mix people usully use and how long cooking time. (ii have one deep tin)
I will be making a normal sponge mix and will be using a gas oven.

my most popular cake is a 10" round that i usully use two tins and split a 12 ounce mix between the two then cook on 170 for 25-30 mins.

http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

IV BEEN LOOKING AT THE BAKING STRIPS TO HELP COOK MY SQUARE TIN BUT THEY ALL SAY THERE GOOD FOR ROUND CAKES? IS NEWSPAPER ANY GOOD TO WRAP AROUND MY TIN?

I would not mix heat and newsprint!! Even if you wet it it will dry out fast. Just guessing that the ink is probably not food safe either. It might even smoke and cause fumes. Pin the strips tight, they should stay on as well as anything else!

Those stipes can be used on any shaped pan. Just pull them tight and pin them together.
DO NOT use newspaper! I am not fimilar with 12 oz mixes and how they fill a pan. If the batter comes up the sides *at least* 1/2 way it will be fine. If not you need to add more batter. I'm thinking you are going to need at least one more mix.
Here in the US our mixes are 18 oz; a 12" sq pan, 2" deep needs 2 of those.

Thankyou for your comments, i only suggested newspaper as i read that from some other forum that someone had used that to help cook the cake more even.