I look for jackets, or parkas, that have waterproof zippers and no flaps so there is no place for rainwater to collect. I prefer taped seams but silicone sealed seams can be effective.

I like DWR because it is the most practical and breatheable, plus DWR is renewable with McNett or Nikwax spray-on or wash-in products.

If you can purchase a DWR jacket that suits you, do it.

If not, DIY may be feasable on a suitable nylon-fabric jacket.

Here is a link to my DIY/MYOG page to fabrics and patterns for backpacking clothing and gear.