You don't want to download hacks and cheats, yet you want to build up a character without playing it. Only see one way how you would do that without a cheat program. Use a memory debugger and modify your character in memory. SoftIce was the big one years ago, Code Myster made his own little version that I enjoyed using. You can program your own in C++ using MFC as it has ReadMem\WriteMem functions in it, just need to find the handle of the program (simple to do). Of course, by the time you figure all of that info out, you might as well have just played to get there.
A level 40 character can be made in about a week of good solid playing. Level 30 is possible in a few days. It's 45+ that takes the longest (more experience to go from 49->50 than from 1->48 if I recall correctly). Chances are you will have found better items by the time you get to where you were again anyway. Just play multiplayer. More flexibility. Single player is fun for a romp every now and again, but multiplayer really is just easier to play with.
A level 40 character can be made in about a week of good solid playing. Level 30 is possible in a few days. It's 45+ that takes the longest (more experience to go from 49->50 than from 1->48 if I recall correctly). Chances are you will have found better items by the time you get to where you were again anyway. Just play multiplayer. More flexibility. Single player is fun for a romp every now and again, but multiplayer really is just easier to play with.