New tree surgeon harnesses can be very expensive typically £150~£200 and at least £50 for a used one. For small and occasional DIY jobs a cheaper alternative I use is to make a harness out of car straps by copying the basic design setting of the expensive ones. The straps can then be reused for their original purpose.
Keep in mind that what follows is not the best possible solution and you do this at your own risk. I decline any responsibility of any harm or injury or damaged caused by the use of such method.
make loops on the straps (straps like http://www.s2as.com/p-Dakine_Tie_Down_Straps_12_2011-3973.aspx) as indicated, (position depend on body and legs size) the loops are needed later to keep the lateral downward ones (wihout loops) in position. one strap with 2 loops, 2 straps with one each , 2 strap with no loops, length at least 2 .5 metres
wrap it around the top of the thigh with 2 or three rounds keeping the loop on the outside
and then secure it THE RIGHT way, test it by pulling it near the latch
same on the other thigh, symmetrically. Pay attention to your testicles the last thing you want is the strap to press hard on them should the need to stop a fall occur.
fit the 2 loops strap around the waist, 2 or 3 rounds
connect and secure the waist and thigh straps using the loop as a guide NOT as support, in other words the 4th strap must embrace all the rounds of the leg and waist strap. The loops are meant to keep the connecting strap in position
you can keep the excess of the connecting strap inside the pocket
same on the other side, the harness is now ready. you might want to add a third loop by the latch, centred to the middle of the belly to guide the rope or strap that will secure you to the tree (not shown here)
done today and the harnesss worked really well, do not be tempted to play Tarzan though