A custom sheet metal fabrication project should always start with a concept, or an idea of what you want built, and how you'd like it to look, and this by itself can take days, or even weeks, because it's best if you make your mistakes during this stage, here they won't cost you money.
You don't want to make mistakes that waste the sheet metal, or a lot of your time, so during the first stage of this venture, take a lot of measurements, and draw up a lot of concepts, and make them out of cardboard if you need to, but take your time here.
Once you have a solid concept, you can plan out how much sheet metal you need to complete the project, and then double it, you can't go wrong with extra sheet metal, now that you have your metal, you can lay out your project on it, using the cardboard cut out that you made, trace around the outside edge after it's laying on the sheet metal.
Once you have that done you can cut it out and begin to make your bends, get the basic idea bent in the metal, you can fine tune it from here, bending more in some places, and less in others, making bends sharper, or more round, adding body lines or crowns in the metal.
After you have a basic idea bent in to the sheet metal, you can finalize things a bit more and get it ready to put on your car, if you need two of the same part, you should make the second part now so you can just go to town and get the entire job done at one time.
Now it's time to put the parts on your car, and this can be nerve racking, so make sure that you do it right, take perfect measurements, this is the part of the process that will make or break the entire project this part is absolutely crustal to the out come of your project, so take your time here.
I've been in the automotive business for about 20 or 25 years, I have worked in all facets of the industry, from parts to restoration, all different makes and models, I just want to keep people interested in the old cars because it's where my heart is.