"And the expenses, such as interest, taxes, materials, tools, etc. Would I just deduct them as I usually would on a Sch C?"

No.

Understand that those are not expenses. They are invested in the project(s). You have multiple projects, so that means a holding period for properties that get listed for sale, and over the year end, the invested costs are inventory (in the asset). That includes, for example, engineering, drafting, permits, etc. He needs to break down everything by property. This is called CIP = construction in progress. It isn't amortized. It's held until sale date, then the CIP is COGS, along with selling costs.

There will be some operating expenses, such as worker comp insurance or licensing, and some hand tools and consumables (no different than office printer paper, as an example). Any larger equipment, like a construction site trailer or a highlift, are part of business assets. But, another example, renting a highlift or cherry picker or crane to fly in trusses, etc, would be tracked by the project, not as part of operations. Paying subcontractors = project specific. That also means 1099 issues, lien releases, oh what fun.

Any project he then decides to rent out is treated differently, too. Now he is using that asset in operations, so it becomes a fixed asset, not an inventoried asset.

You're going to want to get up to speed on construction and flipping. Based on: "buying and selling in under a year on a few homes to start with" that is operational as Sched C, not investment as D.