I'm planning on buying a shed and summerhouse online, and had been intending 
on siting them on a solid concrete base.  Now the total cost for the garden 
is going too high and I'm wondering if the concrete bases are a luxury I can 
do without???

Unfortunately I know NOTHING about the subject but I know you guys do :-) 
I'd be so grateful for any suggestions for alternatives.

FYI the shed / summerhouse are:

http://www.gardenbuildingsdirect.co.uk/Summerhouses/Waltons-Sussex-Summerhouse
http://www.gardenbuildingsdirect.co.uk/Timber-Garden-Sheds/BillyOh-Shed