|>>|| No. 6143
As others have said, unless you're a particularly odd shape, buying off the peg then getting it fitted at a seamstress is likely a much better idea and will look exactly as good.
Even with accurate measurements to give, I don't think I'd want to rely on a suit being sent to me I've never tried on - even the worst alterations shop will at least be able to see how a suit wears on you in real life, and can adjust accordingly.
Unless you're really set on the idea of choosing your own fabrics and so on, I'd advise against it.
Whichever way you go though, I'd also recommend getting your shirts fitted too. That was a game changer for me.