Welcome to AudioCircle Jreb!
Check out Hawthorne Audio for parts/kit to do what you want, and also Troels Graveson OB-15 speaker kit.
If you want to design from scratch, the AE Speakers Dipole series of driver is intended for open baffle use and are very high quality speakers.
To learn a little about crossover design, read the loudspeaker cookbook, or search for crossover design articles on the web. Crossover is the heart of the speaker, make or break, and there are lots of non-intuitive concepts to understand and blend together to find a make a good design.
Rich