how to start to design arm boards

[mrm]

hi,

i'm beginner in embedded system and arm. i worked with this system for last four month.
now i can use embedded boards like raspberry pi to install linux and others, but now i want to design my board with arm cpu. i want some resource about that.

for example, how can add flash memory or ram to arm microcontrollers?
or after designing board is linux driver programming needed or hardware they has drivers for linux ?

excuse me for my poor english
thanks in advance