apparently, I can't deduct any of those expenses until the rental is actually completed and ready to rent.
That is correct. I am also assuming this is a vacant lot. You probably paid for things like land clearing and leveling. That's what I'm presuming. That would be what's referred to as a capital improvement; also referred to as a property improvement.
Understand that property improvements are not deductible. At least not in the sense that the word "deductible" is defined and understood by most. Your improvements add to the cost basis of the property. So if you paid $10,000 for the land and paid lets say, $2,500 to clear and level it, that makes your cost basis in that land $12,500 now.
Typically, capital improvements (property improvements) are depreciated over time. This basically allows you to "deduct" a small amount of your cost basis each year as the property is "in service" as a business asset of some type. This "deduction" is referred to as "depreciation". In your case, that would be a rental business asset. For rental property the established depreciation period is 27.5 years for residential rental real estate. Also, you are required by law to take that depreciation every year the property is "in service" as a business asset.
The downside of this is that later in the future when you sell or otherwise dispose of the property, you are required to recapture all depreciation taken on the property and pay taxes on it in the year you sell or dispose of the property. Again, this is required by law and we have no choice in the matter. (there are exceptions - but I'm not getting into that now in the interest of simplicity.)
Now that you've read and hopefully understood all the above, here's the real zinger. When it comes to residential rental real estate, land is not a depreciable asset. Therefore you will never at any time depreciate your cost basis in the land. Once you build or locate a structure on that land and classify it as a rental asset, then your cost of that structure will be depreciated over time.
