How can an individual build its Portfolio? Can the internal rate of return be determined without considering net present value?

Portfolio is build based on individual risk and return preferences. 

 

IRR is where NPV is equal to amount spend. 

Answer to Question1: Building a portfolio is an Art.
Your need to measure the return that you are expected to take and when you need the return (time duration).
Since everyone invest by expecting a return on a specific time perios.
This could be longer term as well as shor turm.
For an example equity vs fixed income.
Equity gives a short term return and fixed income is for longer term. 
Generally equity carries a higher returns while fixed income is low.
The time duration that you expect your return is an important factor.
In addtion to this it is important thing consider is the risk that you willing to take.
Every investment carries a risk.
Depending on the risk apptite you can go for high or low risky investments.
It is always better to have a pool of investments rather than having a one investment(building portfolios).
There is a saying of "always better to put eggs in different baskets rather than one." The segregation of investments is entirely depending on the risk, return, expected time duration, likes and dislikes and the amount you posses. 
  Answer to question
2- Internal rate o return(IRR) and NPV both use in investment appraisal.
NPV measure the return based on todays values and IRR measure the minimum return expected in order to make project viable.
(to make NPV zero).
How ever in financial world NPV is superior than IRR.
Hence you should give priority for NPV.
Secondly you can consider IRR.
 

NPV is the difference beteween the present value of future cash flows arising out of a project and the present value of investments.

IRR is the rate of return at which NPV =0

In other words, you will get what you have spent on the project. 

For finding out IRR, you have to keep NPV=0 and the find out the rate through Trial and Error method..

If a project has positive NPV, we can go for it given that IRR>cost of capital

Now if NPV and IRR are contradictory to each other, go with NPV value

Now coming to the other question, individuals' risk taking ability decides the portfolio composition as well. When we go for preparation of portfolio, we must consider the risk tolerance of the investor and must decide how the portfolio must be diversified.