So how I should calculate 40-50% gross rentals for operating costs are beyond me.

The rental property analysis tool will calculate all of this for you:http://www.biggerpockets.com/recritic.html(It's not a replacement for tax advice, but it can help you better understand the calculations and let you see what happens when different assumptions/values change.)

thanks all - now since its a numbers game I want to create an excel sheet I would like to knowhow to calculate mortgage monthly payments, what is the formula - I thin I have it, but when I do it on a webbase calculator - it is off by a couple numbers, I want to know the actual formula to determine my monthlyonce i have that I will input the expenses so I can know if this house is a great investment or notthanks

Its the same formula calculations, but its just coming from different directions.You have to be careful how you factor the numbers or you will start learning about the Please Excuse My Dear Aunt Sally rules.

i don't want to be discouraged but i had no idea finding the right house would be this hard :( would our best bet be hiring an agent?

At the moment I don't know a whole lot about construction; however, I bet if you put together a good team of knowledgeable people it could work.

So many of everyones posts have been a great help already, but you bet, I'm sure I've got lots to ask help on.

Example: 300k down gets you about $400/ month assuming 50% of rent is calculated for expenses.

I'm sure many people have done this, but I'll bet that most of them don't fully understand why they are doing it, and many of them are losing money without realizing it.What's USUALLY in the back of their mind when they do this, but is often subconcious, is that they are COUNTING on the house to appreciate and/or rental rates to go up.

Calculate how long it's going to take you to pay off the points on the refi before deciding.