i think you should go with absolute quantification, by preparing standard curve of known concentration lemda DNA and amplify single copy gene of virus from your experimental tissue. then compare CT value to identify actual quantity of target DNA. 

I want to use SybrGreen chemistry.

@Tejas

But lambda DNA is not infected, how it will be used for standard.

Please clarify.

If you have any performed experiment, please provide me the details of the experimental plan.

lambda DNA can be used as external control

it is just like protein assay by bradford method, in that you used BSA as standard.

in the case of Realtime PCR, standard could be known amount of any DNA material so you could correlate it with your experimental data.

i have performed relative quantification not absolute quantification. 

If you want absolute quantification, you will need a control containing a known amount of virus nucleic acid. These days, the simplest way of achieving this is to get it synthesised. This costs quite a lot, but you get enough material to last a lifetime. If it's DNA, then you can get it cloned in a plasmid. I use Genscript, though I imagine there are other suppliers. Of course, if you can purify your virus in large amounts, you can make your own control for much less money, but obtaining enough pure virus to make measurable amounts of viral nucleic acid requires an ultracentrifuge. 

You don't need to synthesise the whole genome, just the target sequence of your PCR. 

On the whole, I would advise against SYBR-green for quantification, unless your PCR is very clean (no non-specific products or primer-dimers). If you have to use SYBR-green, always run a melting curve afterwards to check that there is only one melting peak. Any samples or controls with multiple peaks should be removed from the analysis. 

What is your virus, by the way?