Can I carry over the 2020 losses to 2021 and use them once I have rent income?

I'm in the data compilation portion of my hunt, and the data I am looking for will result in thousands of items being harvested for digesting and manipulation; my needs require "big data" to be involved and I was really looking for sources like listsource that was suggested by Zachary.

Also add in disposal or storage of items. 

Oftentimes, landlords want to sell when the big items start needing to be replaced, roofs, HVAC, sewage lines, electrical/plumbing etc. 

So, the rate will be probably ~1.25% higher.Don't forget that there is another requirement about being able to carry the mortgage as if the other units weren't rented -- forgot the formal name for this "test." 

The question is whether there is any tax benefits for doing so.You may be eligible for expensing items(if they qualify as an expense).

Vacancy and capex(capital expenditures) big ticket items like roofs and floors.

Apart from unexpected reno costs, carrying costs, closing costs, etc.

To determine if it's worth doing a 4-Plex in addition to the cost you listed, I would recommend looking at; is the lot already graded, and ready for construction, are sewer, water, and gas already at the lot for connection, what type of rents are on your proforma, the biggest one many people forget about are the developer fees charged by the municipality to allow you to build the project, etc.There are a few soft cost items that will be a part of the project that do not get lower just because you're doing a smaller project.

@Naveen Desai you've got some good comments above and just to add one item - as long as your are still claiming your income on your US tax returns you are fine to get a standard, conventional loan.