custom data warehouse in python vs. out-of-the-box ETL tool

[snfctech]

Does anyone have experience building a data warehouse in python?  Any
thoughts on custom vs using an out-of-the-box product like Talend or
Informatica?

I have an integrated system Dashboard project that I was going to
build using cross-vendor joins on existing DBs, but I keep hearing
that a data warehouse is the way to go.  e.g. I want to create orders
and order_items with relations to members (MS Access DB), products
(flat file) and employees (MySQL).

Thanks in advance for any tips.