Feb. 2013:
Ekta Grande started in 2007 and has maintained a steady interest among builders - and for good reasons. These Revelator drivers are among the most diy-friendly drivers ever made. Smooth frequency response from appropriate front panels allow simple crossovers and excellent sound. The 18WU Illuminator drivers may provide increased dynamic headroom compared to Revelator, but comes at extra cost, more than 100 € per driver. A significant increase when we're dealing with four drivers.
The 12M middriver is a darling and an example of excellent performance and delicate industrial design. I don't think it can be done better. The R2904/700000 tweeter is not exactly cheap and you may start out with the R2604/832000 tweeter if budget is tight.

The up-dated version offers simpler cabinet construction compared to the curved side panels of the original. Front panel width has been increased by 3 mm and overall height reduced by 100 mm. The 120 cm height of the original was the most common regret by builders.
The two ports of the former version and their placement were not ideal as the upper port had to be above the mid cab causing some obstruction in air flow, thus one port of 100 mm diameter and 200 mm length, which can be added to the front or rear.
The cabinet net volume is 65 liters minus bracing and mid cabinet so we end in the range of a little above 60 liter. Port dimensions provide a port tuning (Fp) of 33 Hz.
The upright drawing seen below is meant for those you may prefer to build a straight rectangular cabinet and tilt the cabinet by adding different length spikes to the front and rear of base plate. My preference is the right hand drawing where a 5 deg. tilt is built into the structure.

The crossover is exactly the same as before and two tweeter options will be given, no more, so please do not ask for other tweeters. The R2904/700000 and R2604/832000 are so alike that only minor changes to the crossover is needed and the exceptional linear response from both tweeters on this baffle allows very simple crossovers.
Initially a 3½-way crossover, quite similar to the Ekta, was constructed. 4th order to the tweeter and the lower bass working like a semi-sub. This made an even more heavy low-end and all in all it sounded quite nice. Flat response and a balanced presentation of all kinds of music. Playing around with the LspCAD and looking at the almost ideal response of all drivers, the idea of making a minimal crossover was obvious. SPL of individual drivers seen below. Making a minimal crossover would also allow the use of some of the best components available.
2013: I think this choice was right as few builders not having the option of decent out-on-the-floor placement have had problems with excessive bass. 

The crossover is 4 coils, 5 caps and 6-7 resistors, depending on whether the 7000 or the 8320 tweeter is used. I like the 8320 version a lot. Really can't tell you why, but difference in the coating of the two diaphragms may be the reason. The 7000 has a thinner coating, probably providing some of the extra sensitivity and probably reaching a bit higher in frequency response. The 8320 has a slightly "darker" presentation compared to the 7000 and despite the two versions being tuned to render the same frequency response +/- 0.5 dB. The rise in impedance at Fs is much higher for the 7000, thus my guess on a thinner coating.