You're several steps short of looking at Ti/Tv ratios. I'm going to talk about this in the context of cancer, because it's what I'm most familiar with. Your steps will be something like:

• use an aligner (like BWA) to align both your tumor reads and normal reads to the reference genome.
• Use a variant caller (samtools, Varscan, strelka, etc) to identify somatic snvs
• determine whether each of these sites was a transition or transversion, then calculate the rates.

Also, you may know this, but worth saying, Ts/Tv varies between species (not sure what species you are using).

If you have vcf file to annotate use snpEff and in the html report it will show amongst other things the ratio you want.