There is no way to vent my dryer through the floor or wall, is the roof a safe option?

No. Do not recommend using a roof due to the lint build up. What kind of dryer is it gas or electric? If it is gas then absolutely not to the roof. With an electric dryer you can get one of those new gadgets that vent the dryer into the room. It's a big box thing but that lets a lot of hot and humid air into your home and you don't want that.

Just why can't you vent through wall or floor? I'm stumped on that one. Where are you locating the dryer?

There is no way to vent my dryer through the floor or wall, is the roof a safe option?
Yes you can. A friend of mine's dryer is vented through the roof. But I would look into building and city codes before having installed through your roof.

I agree with twinkiedooter there's not enough force or pressure behind the dryer to blow it up a stack in the roof(THE LINT) this would end up being a for sure fire hazard.

You are not supposed to have more than 2 bends in the exhaust line due to the pressure of the dryer not properly venting the air.

Actually you can vent through the roof. First as twinkiedooter said for venting into the room. The box has water in it so the lint is trapped, obviously you need to change the water fairly often, then on the outflow you attach a squirrel fan to boost the airflow up and through the roof. This works and I have seen it done in a couple of places. No lint-no fire hazard-cooler air being pushed through the roof. Sounds like a pain, but if you use just the box to vent inside, then you need a dehumidifier.

Dose the vent bosx work? And dose it hold lint? I do not want to vent it to the front of the house.