Since you are looking to do long term rental, you might need to really assess the real cost of construction. Building for sale product is very different financing criteria than for rental. I realize that you work for a builder and you might be able to save some money but lenders look at market cost as a guide.
If you do for sale product, explore pre sale situations so that when you approach the lender you can show a viable exit. You could also look to do an investor turnkey type deal. Either way, your ltv will be much lower than existing.
With $100,000 you might be looking at $500,000 in existing property where as with new construction, you might be in the $300,000 range. Construction cost, land, carry, lease-up etc will mean that even a really cheap deal would be over $100,000 per unit. With $300,000 you would only be able to do three units. Existing property might yield you 10 good units which will be a lot easier to finance and provide a better return on your investment.
Lastly, if you do have some land, you could phase in the building by building one duplex, leasing it and then refinancing and then doing another and so on.
We currently are building 8 duplexes on a for sale basis and have pre-sold 3 units which made our financing a lot easier.