I've never needed to make 'slipsticks' that engage together with a tongue and groove as shown in the illustration. If I'm building something to go in a large alcove I simply cut four sticks, two for the horizontal dimensions, and two for the vertical dimensions. The sticks are usually plywood or MDF, about 2"+ wide by 3/4" thick. In each case the sticks are a foot or three shorter than the space. For example, if the width is roughly 10', two sticks each about 7' - 8' long work well.
I go on-site with the sticks, masking tape, and clamps of some sort- spring clamps are good, but small F clamps or small G clamps work too, a camera and a profile gauge for cornices and skirting boards. I put the two 'horizontal' sticks together, grip them so they form a straight pair, find the widest point and the narrowest point, marking each across the face of one stick from the end of the other. Clamp or tape the two sticks together at their shortest (narrowest) length and then go up the space marking off significant points on the sticks such as electrical outlets, air vents, etc. Then do the same with the vertical dimensions using the other pair of sticks. It's also important to know which way the sticks fit together - a mark to clearly identify this is easily done. A few photographs complete the survey. Later, when planning the build, use the sticks reassembled to plot out the job, much the same as map grid references I suppose.
The advantage of sticks like this is that they are cheap, and specific to the job. On complex jobs there are quite a few marks on each pair of sticks, and it can be useful to reassemble them in the right order to double check something. Being specific to a particular job means they stay with that job until it's finished, after which they can be recycled or even tossed out.
Alternatively, you can go digital and buy multi-line lasers, distance finders, etc, that do a similar surveying job, as long as you've got batteries or power of some sort. ha, ha. Slainte.