Space colonization one step at a time (Step 1)

If we make everything look complex we will take a long time to colonize
space!

So we should think of one issue at a time.

Step 1. We need a pressure shell.

Once we have a pressure shell we can have a candle light party in the shell
if it has the proper temperature and is filled with the correct mixture of
gases. With luck we could survive in it for say one month if we have brought
adequate provisions along.

What are the resources we need to build a pressure shell 2 Km in diameter
(should it be cylindrical or spherical? Should we build the first pressure
shell in Earth orbit or Moon orbit?). How much will it cost with our present
space capabilities? My feeling is, even the first pressure shell we make
should be sufficiently large.

Regards
Selvaraj