I would like to add a toilet to a 2000 sqft metal building that has only used for storage. I would need to put in septic system and the dwelling is single story building on a concrete slab. Will the toilet need an air/roof vent? Any pointers?

Donka! P2E

Yes it will and as long as you're running a vent you might as well tee off for a sink or lavatory since, with the vent, the drainage's already in place.
The lay outwill go like this. Toilet to septic system, sink/vent to connect to the toilet drain and wet vent it. More questions? I'm as close as a click. Tom

Thanks tom... so this air duct is req'd to maintain a vacuum? For gases? What?

How deep does the toilet drain need to go down below the slab? Is this depth relative to the depth of the adjoining main septic/drain line?

Any feel for the wall mount toilets?

Thanks!

P2E

"So this air duct is req'd to maintain a vacuum?? fo gases? what?
Airducts are heating and AC, vents are for plumbing."

Let me explain about vents. When you pull a plug or flush a toilet the water going down the pipe sets up a suction. This has to be relieved by outside air. Hence a pipe through your roof. If the vent is blocked by a birds nest or a dead critter the water will pull suction through the nearest trap and you will hear a gurgle. It may be a fixture trap or the toilet may talk to you but you will hear it someplace. It is possible for the suction to pull enough water out of a unvented trap to have sewer gas escape And now you know about vents.

How deep does the toilet drain need to go down below the slab?
The drainage can be as close or as deep as you wish under a poured slab.

Is this depth relative to the depth of the adjoining main septic/drain line?
Yes, since this will be the main septic/drain line it is indeed "relative".

Any feel for the wall mount toilets?
You must have strong backing to mount a wall hung and good pressure to activate the flush valve.
Goodluck, Tom