Topic: Build your own mech, yes or no?
Response: Work on it is going VERY slowly in my basement, for lack of parts. They don't stock myomers or ferro-fibrous armor at my local Home Depot for some reason, and I got some REALLY funny looks when I tried to buy a fusion reactor. Not sure how I'll get it out the door if I ever finish the thing.
Seriously though (which in itself is a relatively rare event for me), I design a LOT of customs, but rarely ever use one in a game. I've even got a handful of custom miniatures (scratch built) to represent a couple of them on the table, and built up an entirely scratch-built light 'Mech in roughly 1:72nd scale to go with a couple of old Revell plastic model kits of the old "unseen" 'Mechs.
In some campaigns, I'll make a few small changes to an existing design using salvaged equipment to replace damaged equivalents, which may require a few other tweaks to make fit, but that's not "my own", merely a modification. Fielding a full custom generally doesn't go well, because everyone then has to verify that the design doesn't go overweight for its stated tonnage or violate other construction rules. I've met several players who won't hesitate to build a "75 ton 'Mech" that weighs 80 tons if they think they can get away with it, and several more who simply can't get the math right and unintentionally violate the rules one way or another. Basically, it delays the start of a game while everyone checks the other players' designs for legality. We eventually stopped using customs, but it's a phase that almost every player goes through when they first get into the game.