Edited Date/Time:
Thought I share my YZ 125 project.
The plan is not so much trying to make it fast (I have my 250f for that) but to have a fun project and make a bike that looks and feels "cool" on a reasonable budget... and then shredd that thing on the track 
The starting point is this (see photos below) 2008 YZ 125 i got second hand for 1650 USD.
The engine and the wheels seems to be (knock on wood) good but most everything else needs to be updated.
The budget is around 2000-2500 USD in parts (most are already ordered).
Here's the list of things I plan to do with it:
Plastics
Full Rtech Revolution kit and gas tank - Because I've not seen many cool looking builds with them yet
Cycra Stadium front number plate - Makes every bike at least 10% better looking in my book
Custom graphics (by me) - I'm a designer I better design my own graphics right?
New ribbed seat cover - Comfort and style
New seat base - Current foam is soaked with water and is softer than my sofa
Suspension
Front forks needs to be renovated. Shock should be newly renovated 10 hours ago so hopefully good, needs checking though.
Chassis
Weld crack in subframe
Powder coat frame plus swingarm and triple clamps - Cool factor
Replace some of the bearings - A lot of them are newly changed but some are worn out
Engine
New Piston kit - it's a 125 two strokes, it eats pistons for breakfast
Boyesen reeds - they're cheap but better than stock
Fmf Fatty pipe and silencer - Well let's face it, I want it to be slow so I can feel fast but you can't beat the look and sound of an aftermarket system on a two stroke!
Jetting - duh 
Powder coat covers
Possibly new kickstarter - Rather not spend money on it but I might have to
New drivetrain - Current one is shit
New chain guides - Current one is completely worn out
Brakes
New front disc and pads - check pics, nothing to add
New brakelines front and rear
New Disc protector rear
Controls
New brake pedal
New shifter - current is worn through to the point of it being a hole in it
New footpegs - Honestly just because the current ones look really bad
Emig grips - Love them
Possibly new bars (current are to low)
Wheels
Powder coated
Dunlop mx3s tires - Best tires
New wheel locks
Misc.
Hour meter - Best 5 bucks you can spend
Remove rust from all axles, nuts and bolts - There's lots of it!
Random anodized parts - Bling yo! But only if I can find it at a decent price
Cleaning up everything in general
How it currently sits:
