Another good place to start would be Invalid Link Removed.
Simple, well engineered plans in a kit that puts all the odd pieces in one purchase for you.
The customer service with that website is top notch.Whenever possible I buy from him.
The speaker hardware kits are pretty great, but I'd start with a Jack as opposed to a simplexx. The simplexx aren't bad, but many recommend building the jacks instead.
That said, however, I'll fill OP in on the BFM and Greenboy stuff. Bill Fitzmaurice, also called BFM, sells his designs for speaker cabinets for money, not too much if I recall. His designs are unorthodox compared to most because they use horn loading techniques. It works on the same principle as a musical horn does (like the trumpet or the trombone), they can be a lot bigger, heavier, and harder to build/design than their more conventional counterparts - but they have increased sensitivity and efficiency as well. His simplexx series are more conventional boxes as well, though they're very well designed conventional boxes. In a nutshell, Bill Fitzmaurice's designs tend to use horn loading to help you get the most out of a few drivers and a few watts.
Dave "Greenboy" on the other hand, has designed a number of cabinets, but some of them - the fEARful line - have been released as DIY designs. Those were his first designs and they were always free and DIY. The fEARful cabinets are also a bit unorthodox, though less so than the BFM cabinets, in that instead of a 15" + horn cabinet, you get a 15" or 12" subwoofer using a top-of-the-line Eminence driver, paired with a 6" midrange driver, depending on the design it can be either an eminence or an 18sound midrange, and an optional horn tweeter, paired with a very well thought-out crossover. Compared to the BFM cabinet, it will be a smaller, easier to build cabinet, but it will also be rather pricey - given that instead of having a range of speakers to choose from, you'll have to buy specific drivers, and they won't be too cheap (I've looked up the cost of getting those drivers in Canada). However - they'll go very loud, and very low, and stay very clean with a lot of power.
If you pick either one of those, you definitely can't go wrong, though they're both a bit unorthodox compared to the "410+horn" configuration - that's because the whole 410 thing doesn't throw the higher end of your sound around the whole room evenly, it's best to have your speakers placed in a vertical line on the baffle as opposed to side-to-side like on a 410. If you want a more conventional 410, then Eminence's website does have recommended speaker cabinet designs on their website - you can look up the drivers, and simply multiply the cabinet internal volume and ports by four to get an approximation of a 410. From there the external dimensions, and bracing and such can be worked out by preference. There are some other designs as well, like John_k10's 215 build - which you could take some notes from as well.
Edit for another option: make a 410 with a .5 alignment. This means that two vertical drivers will have an inductor, which is a component in crossovers that filters out high-end, wired to them. This will cut off the high-mid and high-end from two of the tens, so that the two vertical tens left over will throw around their mids and highs better.
