Building a RDMS is not trival, you need to combine classic CS knowledge from several fields together with deep knowledge about harddrives, OS specifics, filesystems, memory, cpu, caches to make it efficient.
A good article about architecture we are required to read is:
http://www.nowpublishers.com/product.aspx?product=DBS&doi=1900000002
For theoretical knowledge about databases I would recommend to buy a book on this topic, I can only talk about the book I use for this, which is Database Systems an Application-Oriented Approach by Kifer, Bernstein and Lewis.
You might want to look at some opensource databases for ideas.
