If your pup want to be outside to potty and does so willingly than he off to a great start to being fully potty trained. It seems as if he knows when and where to do it, you just need to teach him to do it quickly and on command. I don't know why you would need the sod if your pup already know to and want to go outdoors to do his business. If you limit his intake of water and food during the day that will limit the amount of times he will need to go potty when you are at work. Once you feel confident that he can and will hold it until he has access to the outdoors that is when is will be time to allow him full run of your home. So, I would suggest that you slowly start moving his pee pad closer and closer to the door that he uses when its time to go outside and start teaching him to go out every single time. Only using the pee pads as a back up and not intended for every day use. You will also need to be very aware of his 'tells" for potty time. What does he do right before he goes pee or poo. Those are the signs that you will need to look for when he is roaming free in your home.
Or you can teach him to come to you when he needs to go out. I've taught all of mine at a very young age how to come to me and let me know when they need to go potty. You can find how I did it no my web site:
www.dawnsyorkies.weebly.com/training-tips