I've found that I sometimes need to print very long objects in my 3D printer. The usual way of printing objects that are big in one dimension is to use a delta printer; there's pretty much infinitely extendable in the z direction. This is not the ideal solution for a lot of prints, and I'd rather have a printer that's very long in the X or Y axis.
Therefore, I need to design a printer that is 30 cm in the x axis, 100 cm in the y axis, and about 20 or 30 cm in the z axis. That's 60 liters of volume.
You can just buy a milling or carving machine that's a meter long. There are also 3D printers that have a square meter build footprint. I'm not concerned at all about extending a printer axis to a meter long.
By far the hardest part of this build will be the heated bed. I'm of the opinion that you need a heated bed for a 3D printer, and with a bed this big, it will be a challenge. The rule of thumb for a heated bed is 0.6 W/cm² if you're printing with ABS, and my print bed is 3000 cm². This means I need an 1800 Watt heat bed at the bare minimum. That amount of power means a crappy heat bed, and ideally I would have 1.0 W/cm². That's 3 kilowatts.
I'm trying to build this thing for less than $2500, which means a DC powersupply for the heated bed will take me over budget. I'll need to do an AC heated bed with an SSR. This is well-tread territory in the Reprap world.
That amount of power means a 25A circuit with 120V. This means I won't be using it at home. I'll be using the 220 mains at the hackaspace. There it will only be 13-14 A.
Therefore, I need to find a silicone heated bed, 30cm by 100cm, rated for 220V. Like this, but a lot bigger: