Choose your lumber depending on the desired height of your standards. Keep in mind that the taller the standards, the heavier they will be to move. You also don't want to drill holes all the way to the top of the standards because it will make the jumps top heavy and less stable. Buy pressure treated lumber to withstand the elements.
For 4 foot standards, purchase 8 foot long 4' X 4's and have the lumber yard cut them in half for you. That makes it easier to transport them and also saves you having to cut them when you get home. For 5 foot standards, buy a 10 foot long 4' X 4's and for 6 foot standards, buy a 12 foot 4' X 4's. To make the base, you will need one 2" X 8" X 8' for each standard. You will also need at least two 3/8" X 8" carriage bolts, nuts and 4 washers per standard.
Measure 3 feet from the bottom of the 4' X 4' post and mark with a dot. Mark 3" increments above and below the 3 foot mark, with the lowest marking at 18 inches. Do not drill holes on the top 6" to 12" of the post.
Use a measuring tape to mark a cross 2" from the edge of the post. You want to center each hole in the middle of the post.
Using a 5/8" spade drill bit, drill a hole through each cross mark. Be sure to keep the drill bit straight while drilling or the holes will be crooked. You can also mark both sides of the 4' X 4' post and drill halfway through on one side and then turn the post over and drill half way through from the other side.
To make the base, measure four 21" lengths on the 2" X 8".
Mark 2" up from the bottom of the base.
Mark 16" from the end on the top side of the base.
Draw a diagonal line from the 16" mark on the top side to the 2" mark on the bottom side of the base.
Using a circular saw, cut the 2" X 8" vertically at the 21" length.
Cut the diagonal line.
Line up the 21" long base with the bottom of the 4' X 4' standard
Mark the spot on the base piece where to drill the hole.
Drill hole using 5/8" spade bit.
Place base piece on top of 4' X 4' and mark on the standard where to drill hole.
Drill hole through the 4' X 4' standard
Place the base piece that will be on the opposite side of the standard under the standard and mark the spot where to drill.
Drill hole in base piece.
Set both base pieces opposite to one another on the standard and secure with carriage bolt.
Line up the remaining 2 base pieces and mark drill spots on the pieces and the 4' X 4'. Repeat above processes for base pieces and standard.
I have found it helpful to match the base pieces to the jump standard side by assigning a number to each base piece and the side of the jump standard that it goes with.
I stain my jump standards with Behr solid stain in white. No need to scrape when they need repainting, just add another coat of stain.