On Sunday, 13 January 2019 14:03:06 UTC, Chris Green wrote:
We're planning to build a balcony/decking outside an upstairs bedroom
and need some pointers on how to go about designing it as regards
sizes of beams, depth/type of piles required, etc.

Regulation K2 (a) (b) prescribes various situations where
guarding should be provided to areas where people have
access: this can include both internal and external areas.
It states that any stairs, ramps, floors and balconies and
any roof to which people have access shall be provided with
barriers where it is necessary to protect people in or about
the building from falling.
Approved Document K2 (3.3) is quite specific in commenting
that horizontal rails for guarding should be avoided and any
construction should be such that a 100mm sphere cannot
pass through any opening in the guarding.

https://www.labc.co.uk/sites/default..._balconies.pdf

See also
https://www.designingbuildings.co.uk/wiki/Railings
https://www.designingbuildings.co.uk/wiki/Stair_design
(although this is not an authoritative source)

As far as RSJ and foundation piling is concerned, that's structural engineer territory. If you're anywhere near central Scotland or Milan, I can suggest one :-)

Owain