Using an established design and sourcing the appropriate components, or getting a kit of parts or even the wooden panels pre-cut for you is the shortest and safest route to build something that works satisfactorily, with the rating being a lot dependent on what you pay for the parts. Driver prices may range by a ratio of up to 4x from acceptable to good.
If you are good with woodworking and have the space to make lots of sawdust, you can cut the panels yourself and only get the drivers and crossovers (or pcb/parts).
There are a lot of challenges until you build a pair of loudspeakers, even with the whole set of parts in front of you as a kit.
Glueing, tightening, straight corners and airtight construction isn't hard but takes practice. If you don't have those skills mastered, you may want to start with plain panels rather than (more expensive) CNC cut and tapered parts.
The other way to go would be to start from scratch and have fun. You should not be expecting to build a reference quality unit on your first attempt but that doesn't negate the fun you can have while doing so. I you decide to take that route, I would suggest you get a copy of Vance Dickason's "Loudspeaker design Cookbook, 7th edition is the current one. I had previous experience from my youth, both in woodworking and the design process but I read that book from cover to cover several times a few years back and every time I read it I understood and learned something more.
Mixing and matching the drivers, is one important first step. With a two way system you have one point to make them meet. With a three way design, you have to points (crossover points) and three drivers to choose so that they match in sensitivity and crossover points.
The woofer (and midrange) are air loaded drivers and need a cabinet. For simplicity, let's focus on sealed. WinISD and several other freeware programs allow you to simulate the loading of the woofer (or midrange) and decide on enclosure size. Woofers from 8-12" usually need from 25-80lt. The midrange, unless it's sealed in the back with a limited, private air cushion in it's back, will need its own mini enclosure was well, usually from 1-5 lt. The tweeter just needs a hole on the front panel to make the magnet fit inside.
For the enclosure you need to consider bracing (hardwood sticks glued on the panels or fixed against facing panels) and padding with absorbent material that helps to somewhat absorb standing waves inside the enclosure and also (somewhat) increase the effective loading volume of the enclosure.
To make the cabinets you need space, a sturdy flat bench (actually the smaller the better as big ones get full of clutter), tightening screws, dowels if you like,a drill, and the usual tools for carpentry.
It's better to have the panels cut in the shop at the sizes you want so they are better cut and at 90 degree edges. You can do that yourself if you have a good table saw. A good quality jigsaw may do but you need a steady guide. A router is nice for cutting the driver holes but a jigsaw can be also used there (as can a router, but that adds quickly to the list of electric tools and the amount of fine dust).
Crossovers are a big chapter of the effort, whether you go passive or active. You can go the best route and get a digital active crossover (like minidsp) and three amplifiers (they could be gainclones or something like that) and experiment or go passive. The best approach, although not widely popular, is the active way for many reasons. Passive crossovers are explained in books (and the Cookbook mentioned above) and they are simply filters with slopes of varying intensity. They also come with their imprefections and issues that needs to be addressed for each. One could start with a plain crossover after choosing the appropriate "crossing" frequencies and build a low pass filter (for the woofer), a bandpass for the midrange and a high pass for the tweeter. Depending on the drivers you may need to have an increased slope (or order) which adds more components. These components are bulky sometimes and can be very expensive if you go crazy.
And if you put yourself your own design/idea, you really need some means to measure that. Ideally one needs access to an anechoic chamber but since none of us do, there are compromises and alternatives. But they include at the very minimum a good measurement microphone, a suitable preamplifier / power supply for it and software for the computer platform you are using.
Sounds much and complicated? It's because it is. But it's not something that cannot be understood and you don't really need maths skills to build a speaker. And you get a lot of satisfaction from doing that, if you don't mind wasting some wood from time to time, either because it wasn't cut correctly or because it was not put together correctly or because the design idea wasn't good to start with.
I suggest you start with the cookbook above. Read it, understand the process and then you will know more about loudspeakers. At that point you will either appreciate a ready made one or you will have your curiosity and imagination ignited and start putting together tools and drivers.
I think a table saw is the way to go, but IMO a really good radial saw with a clamped straightedge is better than a cheap plastic table saw.
