Oracle Database Discussions

How do I find the the total memory available for oracle to use, so that I can show a user how the memory usage of oracle.

Im in the process of writing an app for a college project that will show a user the state of memory being used in oracle, like when you click on the Administration->Memory buttons in oracles web application. I've already got the SGA and the PGA being used currently, through the following sql statements,

SELECT SUM(value) FROM V$SGA

and

SELECT SUM(PGA_ALLOC_MEM) FROM V$PROCESS

but I would like the final bit of the jigsaw.