I have done a few, they are the same as a right hand rifle.
First figure what you want to end up with and how much money you have to spend.
The action in a Rem 700 in 7 mm mag is considered long action magnum, you can see what cartridges are compatible
here
As for blueprinting I have left that decision to the gunsmith - do it if it needs it. There may also be work required on the action to make a different cartridge feed dependably.
For a new barrel you need to choose brand, caliber, twist rate, contour, length, finish - these would be based on your decision of what you wanted the rifle for.
Timney triggers are great, the gunsmith can fit this at the same time as they were fitting the barrel.
Stocks, in composite I recommend HS Precision or McMillan, stay away from Bell and Carlson as they fit poorly and warranty is a huge pain in Canada.
Barrels start around $400
Barrel chamber, fit and crown $250
Action work starts around $75
Stocks start around $500
Timney trigger ~ $150
By the time you add tax and shipping you are slightly north of $1500 for a basic build.
Dan