We built one and lived aboard for a year then have been cruising for over a year with it. We are very happy with it. Here is our blog https://raindogps34.wordpress.com/head-project/
I need to update the blog but you will get a good idea. When you go to this page the first post will ask you to link to the new page, don't. I haven't done anything with the new page and my darn iPad
freezes up every time I try to erase the link grr.
Anyways, If you build a dry head just be sure your pee and poo tanks
are removable. If you install a tank that cannot be removed it no longer is a Type III MDS toilet and then your homemade toilet needs to be approved by the coast guard( how that's done I have no idea). We use gallon jugs for the pee collection and a 3.5 gal Rubbermaid bucket for the poo tank. Pretty simple
Ours cost $290 to build but $90 was for the urine separator, you could find one much cheaper ( Amazon sells em).
If you have any questions feel free to pm me here.