PIC18 USB Programmer

Hi there ppl.

Im here wondering if could I design my own PIC18 usb programmer. I chose this PIC cause it already has the usb hardware on it so its gonna be easier to assembly the parts.

But as Im kinda noob, I want you guys to tell if am I wrong or not on this:

If Im gonna create a new programmer board from scratch but I dont wanna create a software also, I need to make the board compatible to known programming softwares (Icprog, to me). But how can I know if my board will be compatible to the programing software logic? (Or theres no way to create a totally new board, and we can just modificate the existing ones ?)

So my question is: What are the patterns used to create a programmer? Is there a specific "check-list" or I just need to worry about making my hardware to work? (I dunno if you guys could understand me, I meant as following the usb specifications, filtering noises, ending transmission lines correctly, powering correctly, etc..)

Thank you, guys.
Cya!

With latest PIC programmer pricing, it just doesn't worth to create it. However, PICKIT 2 is a kind of open source (at least 100% on the PC end), they give the bootloader .HEX and the related schematic, so you could build it yourself... but I don't believe you'll beat the already assembled pricing (~40USD$).

Look at Bluerooms electronics JuneBug, which is a PICKIT 2 + nifty development board.
http://www.blueroomelectronics.com/Junebug.htm

There's also load of clone available, but the pricing is not that much under a Genuine Microchip one, and some have their own issue.. as per we see on some forum here and there.