Here is more clarification on how to interpret executive summary report
It is not possible to make an assessment of SGA size using only PA reports. PA reports provide a number of data points which can be the basis for further investigation by the customer DBA. Does the customer have Advisories? if so, Advisories under "Reduce Contention" tab talk a lot about Shared Pool, Redo latches and Library cache - all related to SGA.
A quick look at the Report suggests that to assess SGA size, customer needs to look at the various pools of SGA - database buffers, log buffers, large pool and shared pool. One good thing I notice is (a) there is no SGA swap and (b) Cache Hit ratio is high - these two indicate that most of the SQL statements are being reused from Library cache.
But there are other areas of concern - BufferWait shows there is some contention in accessing database block buffers. While this figure is not significant for a heavily used DB, still it may be possible to decrease this by increasing the size of DB Buffers of SGA. Similarly there is Redo Wait and Latch Wait.
These figures have to be examined with the overall activity of the System and PA Advisories are a good place to start. Beyond this, DB and SQL Tuning is a iterative fine-tuning process and needs to be addressed by DBA.