the below is from the FA
269.3. Indoor area for training and the playing of matches
Note: ideally a Club’s indoor facility should be located at its principal venue for the
coaching of Academy Players but it is accepted that a number of Clubs have existing
indoor facilities which are located elsewhere. Provided that the Rules relating to the
maximum travel time from an Academy Player’s residence to the coaching venue are
complied with, this is acceptable However, it is recommended that any new facility is
located at the principal venue.
Categories 1 and 2 One indoor pitch measuring a minimum of 60 yards by 40 yards which
shall be owned by the Club (or alternatively the Club must have a legally
enforceable agreement with the owner of the facility for its use by the
Club, expiring not earlier than the end of the current Season) and
which
shall be for the exclusive use of the Academy at all times. (Note: an
indoor pitch which complies with the size requirements set out in Rule
I.21 is recommended)
http://www.thefa.com/~/media/Files/PDF/the-fa-2012-13/2012-13-rules/youth-development-rules.ashx