Following are the plans I used to begin with. Instead of using 2x4s, I now use 2x8 Yellow pine. I haven't made a set this way yet, but, next time I will adjust the 1 1/8" width, slightly narrower, so that there is not a left over piece of 2x8 when I'm done. Hope this helps, and good luck. Kentucky Chair Plans Be sure to read through the plan completely before starting to cut or construct. The chair is really like a puzzle and can be assembled with a little help from the photo.  Start with three six-foot 2 x 4’s (You could use pressure treated pine). ripped into nine equal 1 l/2” x l ⅛” pieces. This should yield the following: Seat: (A.) 6 pieces 15” long. (B.) 2 pieces 35” long. (C.) 9 pieces 9 ⅝” long. Two holes, 1 ½” from each end. For A and B: Each piece has two ¼” holes drilled in the center of the wider side. Measure from the same end. First hole is 1 ½”, 2nd hole is 12” For C: Two holes, 1 ½” from each end. Back: (D) 4 pieces 31 1/2" long. (E) 2 pieces 29" long (F) 2 pieces 42" long For D,E,and F: Each piece has two holes at 1 ½” and 25” measured from the same end. All held together with 9-gauge galvanized wire. Align seat pieces as: A-A-B-A-A-B-A-A and hold together loosely at top with a length of wire through the upper (1 ½” holes) At the lower (12") holes. intersperse each piece with a length of C. That is: C-A-C-A-C-B-C-A-C-A-C-B-C-A-C-A-C. Wire and set aside. Align back pieces in the order F-D-E-D-D-E-D-F. and again hold together loosely with a wire through the holes are 1 ½” from the end. Now marry the two parts by threading through the remaining holes. with the C pieces acting as the connectors. The new joint should have the configuration C-F-C-D-C-E-C-D-C-D-C-E-C-D-C-F-C. Draw all wires tight. cut off and secure ends. The ends can be secured with cable clamps. A cable clamp is u-shaped and has nuts that tighten the clamp down on the cable. Take everything apart. sand as needed. finish as desired and reassemble.
Buen trabajo
What is the thickness of the chair, is it 25mm * 30mm?
Can I get the measurements for the pieces?
Following are the plans I used to begin with. Instead of using 2x4s, I now use 2x8 Yellow pine. I haven't made a set this way yet, but, next time I will adjust the 1 1/8" width, slightly narrower, so that there is not a left over piece of 2x8 when I'm done.
Hope this helps, and good luck.
Kentucky Chair Plans
Be sure to read through the plan completely before starting to cut or construct. The chair is really like a puzzle and can be assembled with a little help from the photo.

Start with three six-foot 2 x 4’s (You could use pressure treated pine). ripped into nine equal 1 l/2” x l ⅛” pieces. This should yield the following:
Seat:
(A.) 6 pieces 15” long.
(B.) 2 pieces 35” long.
(C.) 9 pieces 9 ⅝” long. Two holes, 1 ½” from each end.
For A and B: Each piece has two ¼” holes drilled in the center of the wider side. Measure from the same end. First hole is 1 ½”, 2nd hole is 12”
For C: Two holes, 1 ½” from each end.
Back:
(D) 4 pieces 31 1/2" long.
(E) 2 pieces 29" long
(F) 2 pieces 42" long
For D,E,and F: Each piece has two holes at 1 ½” and 25” measured from the same end.
All held together with 9-gauge galvanized wire.
Align seat pieces as: A-A-B-A-A-B-A-A and hold together loosely at top with a length of wire through the upper (1 ½” holes)
At the lower (12") holes. intersperse each piece with a length of C. That is: C-A-C-A-C-B-C-A-C-A-C-B-C-A-C-A-C.
Wire and set aside. Align back pieces in the order F-D-E-D-D-E-D-F. and again hold together loosely with a wire through the holes are 1 ½” from the end.
Now marry the two parts by threading through the remaining holes. with the C pieces acting as the connectors. The new joint should have the configuration C-F-C-D-C-E-C-D-C-D-C-E-C-D-C-F-C.
Draw all wires tight. cut off and secure ends. The ends can be secured with cable clamps. A cable clamp is u-shaped and has nuts that tighten the clamp down on the cable.
Take everything apart. sand as needed. finish as desired and reassemble.