Build a track dolly for about £80. This is great for getting professional dolly shots when making your own films.
Total dolly size = 2ft wide x 3ft long.
Type of pipe used for track = 32mm pvc.
Angle aluminum width = 2in x 2in at 3mm thick.
NOTE: Angle aluminum is a lot easier to work with than angle iron - which is very heavy and hard to drill & cut. It also goes rusty and is generally not much fun to handle.
ALSO: Try to get the wheels positioned closer together so they sit on the upper/top portion of the track rather than middle/sides of the track. (Or in other words - go for a small/narrow "L" shape area for the track to sit in)
I found wider-spaced wheels were trying to bend the pipe and make the dolly harder & more jerky to push with weight on it.