Hello

When can you trust a dog.
When we are at work we shut out 8 month Staff in the kitchen. He is is starting to out grow the kitchen but im too nervous of letting run free of the house incase he chews the leather sofa or something else.
Any ideas?

You have to be guided by your own judgement. Has he shown any signs of destruction in the kitchen apart from maybe the teething/chewing stage?
If your kitchen is a decent size and he has a basket with toys there's nothing wrong with restricting him to the kitchen.
The other question you have to ask yourself is whether the lounge is safe for him.  Are there any wires around or anything which he could harm himself with.  Most of the time your pup is going to be sleeping whilst your out.  So it's your decision, but if he's happy enough in the kitchen with his toys, leave him there. It doesn't matter how big your lounge is, he's still not going to get the exercise anyway.
If you've made your mind up to allow him in the lounge, go with your instinct and go for it.  Make sure he has no access to the stairs at all. If you are happy to let him upstairs I would only do it at this age while you are there to supervise.