I wouldnt advise the glass tank at all, I know from keeping my guinea pig for around 9 years that they can start to smell! Not only that it can get real hot and stuffy even though it may not have a lid.
Im not sure if you are in the UK but I have a spare cage my guinea pig lived in sadly though I couldnt send it as its big. I used to keep mine in a indoor cage and then I used to take the top off and let him graze in the grass. I didnt have a run for him but he seemed happy enough, he made it to a good age sadly he died about a month ago and gosh I miss that little guy!
No you couldnt let a guinea pig have roam of your room coz they chew EVERYTHING! so this wouldnt be safe for him or good for you, plus unlike a rabbit that you can train to use a litter tray whilst its out there would be no hope of this with a guinea pig! There would be poopys everywhere!
Anyways im not sure if im way to late to answer you as this was posted a while ago but I thought Id give it a shot, let us know anyway if you got one and how things are :) I added a cage like mine to give you a idea, obviously you would have to let the guinea pig out for a run but maybe you could get a run at sum point :)