How much Sakrete do I need to repair my front stoop?

What is Sakrete? Is it like concrete?

You will need about 24 cubic feet of concrete. The rock and stone will take up some space so you may need less. But better to go with more than less. You can return what you don't use. Do not put sheet metal over the stone. The concrete will just float and crack. You can use either rebar supported by some stones or wire mesh on top of the stone.

While I am sure that the person that suggested the method you describe meant well, it will fail in the short term and certainly not to local building code. Pouring concrete is an art and if not done properly, can cause a heap of very expensive problems to fix. Number one being water intrusion, which could result in mold issues which are costly to repair. Anything that is flush to the home requires a slope away from the structure along with pulling a construction permit. Take these photos to your local permit office (typically housed at City or Town Hall), and tell them you want to do the work yourself and they can walk you through the permit process and give you a copy of local code to follow. I highly suggest renting a cement mixer for this job as mixing batches in a wheelbarrow will be inconsistent and will not cure evenly. Curing typically takes at least 30 or more depending upon current weather conditions. Also you should not pour if it is too hot, as it will crack before it cures. Same goes if it is too cold.

If at all possible, hire out to a licensed concrete contractor and then you will never need to worry about it for decades to come. Worth the investment in your property and it's overall value. Here is how to hire any contractor you will ever need.

https://www.consumer.ftc.gov/articles/0242-hiring-contractor

Sheet metal never is in the equation of sheet metal. The only metal used in concrete is reinforcing bars that help strengthen the concrete. They are placed at several inches apart depending on the amount of concrete and the expected load on top to reinforce the strength of concrete. They are purchased at Home Depot or Lowe's

At this point I would tell you not to proceed with this project, quite yet. If you could please give me a bit more information on some of the present structure that is there.

What was the reason for failure of the concrete in the first place?

Is there an actual lip of brick that was built into the design of the exterior for the use of building this deck/patio/stoop for the side-use support? Or was this a jimmy-rig (made up as the need arises)?

How far down does the brick go on the non-house side? As far as I can detect, the mortar between the bricks on the lawn side, is cracking and not supportive, is this correct?

Things to keep in mind: Sheet metal is usually aluminum sheeting. Significant corrosion of aluminum embedded in concrete will occur. The corrosion will cause expansion of the concrete and subsequent cracking of hardened concrete. Second, if the aluminum is coupled with any ferrous metals, galvanic corrosion will occur also. Translation: not a good idea. Use rebar.

Would you consider a different method (other than concrete) to perform the repair?

It might be less expensive to have a concrete company bring a truck load of concrete to your house than to buy bags of concrete and make your own. Sakrete isn't cheap for large jobs. It would take at least 36 (90 lb) bags to do your job, according to the calculator at Sakrete.com. That's a lot of concrete. And, yes, get someone who knows what they are doing to look into what you really need to do before you do anything else.