OllyDbg keeps list of memory blocks allocated by debugged application in a table of sorted data consisting of elements of type t_memory. You can receive pointer to memory table by calling Plugingetvalue(VAL_MEMORY) and casting result to (t_table *).
t_memory* Findmemory(ulong addr);
void Havecopyofmemory(char *copy,ulong base,ulong size);
ulong Readmemory(void *buf,ulong addr,ulong size,int mode);
ulong Writememory(void *buf,ulong addr,ulong size,int mode);
int Listmemory(void);