Before answering this question, lets have a look at the choices you have
Readymade Suits or Shirts are designed on standard mannequin patterns & produced in the assembly line and as per the latest fads, say 'slim fit' or a low waist.
There is no consideration for your body type, your occupation, social status, comfort etc.
People of the same chest size are bracketed into the same body size irrespective of their age and need. Moreover there is no scope for self expression & personalized details
Either they are very expensive or very bad.
They can be bad even if they are expensive!
There are so many tailors around but very few who understand the styling technicalities, keep track of global fashion scene, carry quality fabric & above all, have a passion for customer delight.
Getting a tailored suit or a custom made shirt is a multistage process: buying the fabric, finding the right tailor, going for fitting & visiting again to take the delivery.
Each stage means travelling to the store.
And if any milestone is missed or garment is not made as per satisfaction then add a few more rounds of travel, which means more hassle with traffic, parking etc. All this is a waste of time, money & energy for you.
Most of the fabric stores (even big brands) have outsourced external vendor as tailor. So even if you buy a quality, branded fabric, the quality of your suit will be determined by a contracted tailor.
Also, there is no product integrity in terms of vision, design, execution.
The fabric is bought from a sales person & tailored separately.