Dog Kennel size help, please!?

I would go with 10x20 if you have the space. My dog has a kennel she stays in during the day while I am at work. It has a concrete pad (6x12) that has a roof over it where her doghouse and water is. The rest is pea gravel (good drainage and keeps her cleaner in wet weather). It is roughly half the size of my backyard. She is also fed there (she eats raw), but sleeps in a crate in my bedroom 98% of the time, and spends the majority of every evening inside with me after I get home from work. I feel there is no reason for a dog to be inside the house when I am not there (they ARE animals, and being outside is actually GOOD for them. It's not like wolves have access to shelter in the wild), but when I am home, she spends time inside with me.