+1.

If you want to make your own frame you have to become an expert in it. This could be theory, but more practically it is to familiarize yourself with the numbers. Since you are designing for yourself you have an easier task in many regards than making a frame for someone else.

The known stuff is dimensions of your wheels. For a first effort you should have the wheels already. Their dimensions affect the amount you can tuck the rear wheel, the BB height, and steering geometry, though fairly slightly. Still, no need to just guess on a custom.

Another known should be the bottom bracket height for your style of bike.

Also, your seat tune angle, and height for the style of bike you ride. This is the main issue, both for determining position in the legs power unit, and also for the frame build.

Then you should know what fork you are using, you should own it, and you should know typically what head tube angle.

Wheel base will probably be specified in catalogs so you want to look at that, but also it is determined by the reach you will need, and this is an item you have to work out from known rides.

You need to study the bikes you own, or can otherwise get a hold of and figure out what the fit is for you. You can also study, or redraw several key frames you are imitating.

You then need to draw out the frame. I think stuff like rattle cad makes it too easy since it is supposed to do some of the work for you. You aren't drawing bike pictures, you are determining the position of parts and the shape of the joints. This does not require a rendered drawing, it requires a full size drawing of the locations of junctions, parts and their relative positions. What you need also is determined by how you build. I only need a few numbers to set up my jig.

Once you start to put this stuff together it pretty much determines itself. Your BB height and seat post angle and length goes in; you postion the rear wheel as close as you want it, then draw the stays. Your front wheel and fork/headtube, headset assembly is drawn. About all you then need to know is how forward or back to move it, then you can draw in the top and down tube. Then you just keep working out the details and coming back at them until you are satisfied, and then leave it and try again later.