Affluent speculator acquiring East German house (9)
I believe the answer is:
'german house' is the definition.
(German parliament building)
'affluent speculator acquiring east' is the wordplay.
'affluent' becomes 'rich' (similar in meaning).
'speculator' becomes 'stag' (type of stock market speculator).
'acquiring' means one lot of letters goes inside another.
'east' becomes 'e' (abbreviation).
'richstag' enclosing 'e' is 'REICHSTAG'.
(Other definitions for reichstag that I've seen before include "German tourist attraction" , "old German house" , "German parliament building" , "diet in Germany" , "Former German parliament" .)