One thing to keep in mind, is that ROAR rules specify a miminum lane width. For 1/10th on-road paved electric and fuel, it's 10 feet. Adhering to this rule helps prevent people from designing tracks that are actually more suitable for 1/12th scale cars.
The farther the location of the track, the wider it should be. In other words, when you're standing on the drivers stand, 10 feet actually looks narrower than it really is. Depending on how far away it is, you may want to make the lane 15-20 feet wide.
Sweeping or technical? It's really up to your club, but make sure you include at least one long straight. Two is good, if you have the space.
Make sure you make provisions for turn marshalls.
Nitro Knowledge Base: http://nitrokb.netne.net
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Kyosho V-ONE RRR WC (x2) \ XRAY T2'007 \ Also owned: XRAY NT1 & Mugen MTX-4