well the cheese stands alone...
Well, not quite alone, since that's my basic choice, too.
I say "basic choice" because I think the
original 4E system got this done perfectly - but very few folk seem to have seen it. "Magic Items" come in two key varieties - those that player characters can make and those that they can't. "Level" or powerfulness or whatever doesn't enter into it; items the PCs can make are regular "Magic Items", items PCs can't make are "Artifacts". "Magic Items" are detailed (along with how they are made) in the PHB (or other "player" book). Artifacts are detailed in the DMG.
For any specific campaign, either one of these classes can be limited or removed entirely. If you want magic items to be exclusively DM toys to hand out as rewards* just don't use "Magic Items" at all; use exclusively Artifacts. If you want the PCs to be the source of any magic item (potentially), don't use Artifacts. It's simple, functional and ultimately flexible. If the "PC made" items have numerical bonuses, though, you'll need some sort of "inherent bonus" option for when you don't use them. Or, you know, simpler option, just don't have them give much numerical bonus...
*: I have to say I'm totally unconvinced, these days, about "magic items as rewards". Rewards for whom? The character? Why should the character be specifically rewarded, exactly? For the player? What kind of a warped "reward" is having an imaginary thing that you can't take out of the game? Is it supposed to be some sort of "Badge of 1337ness" to have a character who has a +2 sword, or something? Good grief.